Patellar thickness and lateral retinacular release affects patellofemoral kinematics in total knee arthroplasty

Purpose

To study the effect of increasing patellar thickness (overstuffing) on patellofemoral kinematics in total knee arthroplasty and whether subsequent lateral retinacular release would restore the change in kinematics.

Methods

The quadriceps of eight fresh-frozen knees were loaded on a custom-made jig. Kinematic data were recorded using an optical tracking device for the native knee, following total knee arthroplasty (TKA), then with patellar thicknesses from ?2 to +4 mm, during knee extension motion. Staged lateral retinacular releases were performed to examine the restoration of normal patellar kinematics.

Results

Compared to the native knee, TKA led to significant changes in patellofemoral kinematics, with significant increases in lateral shift, tilt and rotation. When patellar composite thickness was increased, the patella tilted further laterally. Lateral release partly corrected this lateral tilt but caused abnormal tibial external rotation. With complete release of the lateral retinaculum and capsule, the patella with an increased thickness of 4 mm remained more laterally tilted compared to the TKA with normal patellar thickness between 45° and 55° knee flexion and from 75° onwards. This was on average by 2.4° ± 2.9° (p < 0.05) and 2.°9 ± 3.0° (p < 0.01), respectively. Before the release, for those flexion ranges, the patella was tilted laterally by 4.7° ± 3.2° and 5.4° ± 2.7° more than in the TKA with matched patellar thickness.

Conclusion

Patellar thickness affects patellofemoral kinematics after TKA. Although lateral tilt was partly corrected by lateral retinacular release, this affected the tibiofemoral kinematics.

Level of evidence

IV.     

Decreased ratios of lateral to medial patellofemoral forces and pressures after lateral retinacular release and gender knees in total knee arthroplasty

Purpose

To demonstrate that lateral to medial patellofemoral force and pressure ratios could be a surrogate marker of retinacular tension and patellar tracking.

Methods

The patellofemoral forces of six knees from three fresh-frozen half-body female cadavers were evaluated with a capacitive sensor under simulated operative conditions in six staged clinical scenarios: native knees, knee arthroplasty without patellar resurfacing, resurfaced knee and patella, resurfaced knee and patella with lateral release, gender-specific knee arthroplasty with patella resurfacing, and gender-specific knee arthroplasty with lateral release. Maximum force and peak pressure were simultaneously recorded during three to four ranges of motion. Average values were compared between lateral and medial patellofemoral compartments as an objective measure of patellar tracking for the different settings.

Results

Significant differences in lateral and medial force and pressure differentials were seen in most scenarios despite clinically normal patellar tracking. Lateral to medial ratios of maximum force and peak pressure significantly increased after TKA (2.9, 2.1) and after patella resurfacing (2.8, 2.6) compared to the native knee (1.6, 1.8). Addition of a lateral release in resurfaced knees decreased the ratio of lateral to medial patellofemoral forces and pressures as did gender knee arthroplasty (1.5 and 1.1, 2 and 1.3, respectively). Pressure and force values most closely resembled the native knee in the resurfaced knee/resurfaced patella with lateral release and in the gender knee arthroplasty scenarios.

Conclusions

Use of lateral to medial patellofemoral force ratios as a surrogate objective marker for patellar tracking was validated in this study by decreasing ratios observed after lateral release in TKA and with gender-specific implants.     

Patellofemoral arthroplasty influences tibiofemoral kinematics: the effect of patellar thickness

Purpose

Although controversy still remains, isolated patellofemoral arthroplasty recently gained in popularity as a treatment option for patellofemoral osteoarthritis. It has compared to total knee arthroplasty the advantage of preserving the tibiofemoral articulation, which in theory would allow the preservation of natural tibiofemoral kinematics. Today, however, no data exist to support this assumption. This study was therefore performed in order to investigate the effect of isolated patellofemoral arthroplasty on the native three-dimensional tibiofemoral kinematic behaviour and whether a change in patellar thickness would have an influence.

Methods

Six fresh-frozen cadavers were fixed on a custom-made mechanical knee rig. Full 3D kinematics was analysed during passive flexion–extension cycles, open chain extension, with and without mechanical resistance, as well as deep knee squats, using infrared motion capture cameras and retroflective markers. Measurements were taken for the native knee and after prosthetic trochlear resurfacing with and without patellar resurfacing in three different patellar thicknesses.

Results

Compared to the natural knee, patellofemoral arthroplasty resulted in significant changes in tibiofemoral kinematics, which were most pronounced in the most loaded motor tasks. Increased internal tibial rotation was noted in the mid- and high flexion ranges, reaching at 120° of flexion a mean difference of 4.5° ± 4.3° (p < 0.0001) during squat motion, over the whole flexion range during open chain motion and in deeper flexion beyond 50° (mean at 70°, 1.9° ± 3.7°) during resisted open chain. During squats, also, a more posterior translation of the lateral femoral condyle was observed. The effect was accentuated in case of patella overstuffing, whereas kinematics was closer to normal with patellar thinning.

Conclusion

Isolated patellofemoral arthroplasty alters natural tibiofemoral kinematics, and the effects become more pronounced in case of increased patellar thickness. Therefore, it might be recommended to aim for a slight over-resection of patellar bone if sufficient bone stock is available.     

Medial patellofemoral ligament reconstruction for patellar maltracking following total knee arthroplasty is effective

Purpose

Maltracking of the patella after total knee arthroplasty (TKA) remains a well-recognized problem. The medial patellofemoral ligament (MPFL) has shown to be important for patellar stabilization and reconstructions of the MPFL have already shown excellent functional outcomes for patellar instability of the native knee. Nevertheless, there is only limited literature on using an MPFL reconstruction for correction of patellar maltracking after TKA. In this retrospective study, a consecutive case series was evaluated.

Methods

Between 2007 and 2010, nine patients (nine knees) with anterior knee pain and symptomatic (sub)luxations of the patella after primary or revision TKA were treated by reconstruction of the MPFL in combination with a lateral release. In two cases, an additional tibial tuberosity transfer was performed, due to insufficient per-operative correction. Pre-operative work-up included a CT scan to rule out component malrotation and disorders in limb alignment. Pre- and post-operative patellar displacement and lateral patellar tilt were measured on axial radiographs. Clinical outcome was evaluated using the visual analogue scale (VAS) satisfaction, VAS pain, dislocation rate and Bartlett patella score.

Results

Median patellar displacement improved from 29 mm (0–44) to 0 mm (0–9) post-operatively. Median lateral patellar tilt was 45° (23–62) pre-operative and changed to a median 15° (?3 to 21) post-operative. Median VAS satisfaction was 8 (5–9) and only one patient reported a subluxing feeling afterwards. The Bartlett patella score displayed a diverse picture.

Conclusions

Patellar maltracking after primary or revision TKA without malrotation can effectively be treated by MPFL reconstruction in combination with a lateral release. Only in limited cases, an additional tibial tuberosity transfer is needed.

Level of evidence

IV.     

Patellar morphology and femoral component geometry influence patellofemoral contact stress in total knee arthroplasty without patellar resurfacing

Purpose

The objective of this study was to determine the effect of patellar morphology and implant design on patellofemoral contact stress in total knee arthroplasty (TKA) without patellar resurfacing.

Methods

Radiographic investigation: One hundred and fifty-seven knees of 127 patients were included in the study. Implants used in the present series were Low Contact Stress (LCS), Genesis II and NexGen. The relationship between the pre-operative patellar facet angle and newly identified post-operative osteosclerosis was assessed. Finite element analysis: Using patient-specific patellar three-dimensional finite element models, the relationship between the patellar facet angle and mean von Mises stress within the patella was calculated at flexion angles of 15°, 45°, 75° and 105°.

Results

Radiographic investigation: Post-operative osteosclerosis was observed with decreasing patellar facet angle in the Genesis II (odds ratio?=?0.72; 95% confidence interval, 0.55–0.93; P?=?0.012) and NexGen implants (odds ratio?=?0.87; 95% confidence interval, 0.77–0.99; P?=?0.029). Patients treated with the Genesis II had significantly more advanced osteosclerosis than those treated with the other two implants. Finite element analysis: A negative correlation was found between the patellar facet angle and the mean von Mises stress for all three implants. The Genesis II showed significantly higher von Mises stress than the other two implants at flexion angles of 15°, 45° and 105°.

Conclusions

Both patellar morphology and femoral component geometry influence patellofemoral contact stress in total knee arthroplasty without patellar resurfacing.

Level of evidence

Case control study, Level III.     

Effects of four different surgical approaches on intra-operative joint gap in posterior-stabilized total knee arthroplasty

Purpose

The effects of surgical approaches and patellar positions on joint gap measurement during total knee arthroplasty (TKA) remain unclear. We hypothesized that joint gap changes with different knee flexion angles would not be consistent within four different approaches and two different patellar positions.

Methods

This study enrolled 80 knees undergoing posterior-stabilized TKA. For 60 varus knees, parapatellar, midvastus, and subvastus approaches were used in 20 knees each. For 20 valgus knees, a lateral subvastus approach was used. Component gap length and inclination were measured intra-operatively using a specific tensor device under 40 lb with the patella reduced or shifted laterally, at 0°, 45°, 90°, and 135° of knee flexion.

Results

Mean gap lengths at 45° and 90° of knee flexion were significantly larger with the parapatellar approach than with midvastus or lateral subvastus approaches (P < 0.05). Regarding gap inclination, varus angle increased linearly through the entire arc of flexion in all four approaches. When the patella was shifted laterally, gap lengths at 45°, 90°, and 135° were significantly reduced compared with those for the patella reduced in the subvastus approach, whereas gap length was constant in the parapatellar approach, regardless of patellar position.

Conclusion

Joint gap kinematics was not consistent within four different approaches and two different patellar positions. Relatively large gaps at 45° and 90° were unique features for the parapatellar approach. Surgeons should be aware that the flexion gap is reduced when the patella is shifted laterally in vastus medialis-preserving approaches such as the subvastus approach.

Level of evidence

II.     

Tibio-femoral and patello-femoral joint kinematics during navigated total knee arthroplasty with patellar resurfacing

Purpose

In total knee arthroplasty, surgical navigation systems provide tibio-femoral joint (TFJ) tracking for relevant bone preparation, disregarding the patello-femoral joint (PFJ). Therefore, the important intra-operative assessment of the effect of component positioning, including the patella, on the kinematics of these two joints is not available. The objective of this study is to explore in vivo whether accurate tracking of the patella can result in a more physiological TFJ and PFJ kinematics during surgery.

Methods

Ten patients underwent navigated knee replacement with patellar resurfacing. A secondary system was used to track patellar motion and PFJ kinematics using a special tracker. Patellar resection plane position and orientation were recorded using an instrumented probe. During all surgical steps, PFJ kinematics was measured in addition to TFJ kinematics.

Results

Abnormal PFJ motion patterns were observed pre-operatively at the impaired knee. Patellar resection plane orientation on sagittal and transverse planes of 3.9° ± 9.0° and 0.4° ± 4.1° was found. A good restoration of both TFJ and PFJ kinematics was observed in all replaced knees after resurfacing, in particular the rotations in the three anatomical planes and medio-lateral patellar translation.

Conclusions

Patella tracking results in nearly physiological TFJ and PFJ kinematics in navigated knee arthroplasty with resurfacing. The intra-operative availability also of PFJ kinematics can support the positioning not only of the patellar component in case of resurfacing, but also of femoral and tibial components.

Level of evidence

II.     

The influence of patellar position on soft tissue balance in minimal incision total knee arthroplasty

Purpose

This study aims to clarify the influence of surgical exposure on intra-operative soft tissue balance measurements using a new tensor in minimal incision total knee arthroplasty (TKA).

Methods

Sixty patients with osteoarthritis of the knee received minimal incision TKAs. Twenty patients received a posterior-stabilized TKA using a quadriceps sparing approach, and the other forty patients, using a limited medial parapatellar (mini) approach. After femoral trial placement, soft tissue balance was measured using an offset type tensor at full extension and 90° of knee flexion, with the patella both laterally retracted and reduced. The joint component gap and varus imbalance were used to assess the difference in patellar position and surgical exposure.

Results

At extension, the joint component gap and varus imbalance showed no statistical difference regardless of patellar position in either TKA. However, the joint component gaps decreased at 90° of flexion when the patella was laterally retracted in both TKAs. Additionally, a significantly smaller joint gap was observed in the quadriceps sparing TKA than the mini-TKA with a retracted patella at 90° of flexion. Varus ligament imbalances decreased with the patella laterally retracted at 90° of flexion in the quadriceps sparing TKA, not in the mini-TKA.

Conclusion

Surgeons should be aware of the influence in surgical exposure of the joint gap and ligament balance during patella shift in minimal incision TKA.

Level of evidence

III.     

Patellar tilt and thickness do not influence postoperative flexion in a high-flex design total knee arthroplasty

Purpose

The purpose of this short-term study was to determine whether patellar thickness and tilt influence the postoperative flexion in a high-flex design total knee arthroplasty (TKA).

Methods

Between 2007 and 2009, 106 patients underwent surgery for TKA using rotating platform flex prosthesis (DePuy, Warsaw, Ind). All of them were suffering from end-stage osteoarthritis. All patients were evaluated preoperatively and at 12 months of follow-up. Maximum active, non-weight-bearing flexion was the primary outcome parameter. Standard standing antero-posterior and lateral weight-bearing radiographs were made. The patellofemoral joints were evaluated in skyline views taken with the knees at approximately 60° of flexion. Patellar thickness, patellar tilt, Caton–Deschamps indices and lower limb alignment were measured.

Results

The mean flexion observed before surgery was 125° ± 15° and after 1 year was 128° ± 13°. The mean patellar thickness preoperatively was 24.5 ± 2.9 and 25.8 ± 3.2 mm at 12 months after surgery. The mean patellar tilt before the procedure was 2.9° ± 4.1° and after 12 months of follow-up was ?0.8° ± 5.0°. The mean preoperative hip-knee-ankle was 2.6° ± 6.2°. No significant correlation was found between postoperative patellar tilt and thickness and postoperative flexion (n.s.).

Conclusions

Patellar tilt and thickness after TKA are factors that depend on the surgery. The resection of the patella can influence both patellar thickness and patellar tilt. By developing adequate surgical instruments, it would be possible to avoid the occurrence of an exaggerated patellar tilt or a major difference in patellar thickness. However, these two factors did not seem to influence the postoperative flexion in a high-flex design TKA, which can be seen as one of the most important outcome factors after TKA.

Level of evidence

IV.     

Less anterior knee pain with a routine lateral release in total knee arthroplasty without patellar resurfacing: a prospective,randomized study

Purpose

Anterior knee pain is a major cause of complaint in total knee arthroplasty (TKA) without patellar resurfacing. The concept of improved patellar tracking and decreased retropatellar contact pressure for lateral retinacular release theoretically suggests that patients with lateral retinacular release in TKA would achieve a lower incidence of anterior knee pain when compared without lateral retinacular release. We sought to determine (1) whether those patients who received a routine lateral retinacular release in TKA would attain lower incidence of anterior knee pain as compared to patients who received TKA without lateral retinacular release and (2) whether lateral retinacular release would increase the lateral retinacular release-related complications.

Methods

A total of 148 patients who underwent TKA with the use of the Gemini MK II mobile bearing were randomized to receive either routine lateral retinacular release (intervention group) or not (control group). Patients were assessed by the visual analogue scale for anterior knee pain, the Knee Society clinical scoring system of knee score and function score, and patellar score for clinical function. Patients’ satisfaction and lateral retinacular release-related complications were also evaluated.

Results

The overall incidence of anterior knee pain in the intervention group at 18 months follow-up was 5.6 %, while that of the control group was 20.6 % (p = 0.009). No statistical difference was detected between the two groups in terms of lateral retinacular release-related complications (n.s.), patients’ satisfaction (n.s.), knee score (n.s.), function score (n.s.), and patellar score (n.s.) at 18 months follow-up.

Conclusion

The present study suggests that routine lateral retinacular release can reduce anterior knee pain and does not increase lateral retinacular release-related complications, in TKA with the use of the Gemini MK II mobile bearing without patellar resurfacing.

Level of evidence

Therapeutic, Level I.     

The influence of patella height on intra-operative soft tissue balance in posterior-stabilized total knee arthroplasty

Purpose

Although the patella reduced or everted position has recently been recognized as an important factor in influencing soft tissue balance during the assessment in total knee arthroplasty (TKA), the influence of patella height on soft tissue balance has not been well addressed. We therefore investigated the effect of patella height by comparing soft tissue balance between high [Insall–Salvati index (ISI)?>?1] and low patella patients (ISI?≦?1).

Methods

Using a tensor designed to facilitate soft tissue balance measurements with a reduced patellofemoral joint and femoral component in place, we intra-operatively assessed the joint component gap and ligament balance of posterior-stabilized (PS) TKAs in 30 osteoarthritic patients performed at 0, 10, 45, 90, and 135° of flexion, with the patella reduced.

Results

When comparing the two groups, the component gaps of the higher patella group showed a larger trend than those of the lower patella group, with significant differences at 90 and 135° of knee flexion. Moreover, the joint component gap positively correlated with ISI at 90 and 135° of knee flexion.

Conclusion

Patella higher group showed significant larger component gaps than patella lower group in high flexion angles (90 and 135°). Pre-operative measurement of patellar height can help predict intra-operative soft tissue balance in PS TKA.

Level of evidence

III.     

Dynamic KINE-MRI in patellofemoral instability in adolescents

Purpose

The impact of kinematic MRI (KINE-MRI) in the patellofemoral instability and anterior knee pain of the adolescents is rarely reported. Our special interest was to evaluate the patellofemoral joint biomechanics with KINE-MRI in adolescents with affected and unaffected knees in a case–control study.

Methods

KINE-MRI was performed in 29 adolescents (affected knee group, n = 29 and unaffected knee group, n = 26) aged 11–16 years with unilateral patellofemoral instability. For the control group, we enrolled ten healthy age- and sex-matched volunteers (healthy knee group, n = 19). The study parameters, bisect offset, lateral patellar displacement, patellar tilt angle, sulcus angle and Insall–Salvati ratio at 0, 10, 20 and 30° of flexion–extension, were measured for the affected knee patients (n = 29), unaffected knee patients (n = 26) and the healthy knee subjects (n = 19).

Results

The affected knee and the healthy knee subjects had a significant difference in the bisect offset ratio, lateral patellar displacement test and patellar tilt angle test. In these parameters, the difference between the affected knee patients and the healthy knee subjects progressively increased towards the full extension of the knee. In the affected knee and unaffected knee patients, bisect offset ratio at 0° ranged between 0.50 and 1.20 in both groups, whereas the bisect offset ratio in the healthy knee subjects ranged between 0.33 and 0.75 (p < 0.001). At the 0°, the lateral patellar displacement test ranged between 0 and 10 mm in the affected knee patients and between 0 and 35 mm in the unaffected knee patients, whereas the lateral displacement test ranged between 0 and 5 mm in the healthy knee subjects (p = 0.003). Patellar tilt angle test ranged between ?30 and 20° in the affected knee patients and between ?30 and 24° in the unaffected knee patients, and in the healthy knee subjects, the patellar tilt angle test ranged between 10 and 24° (p < 0.001).

Conclusions

The KINE-MRI was able to detect significant differences in patellofemoral joint kinematics between the patients and the healthy subjects. A new finding with clinical relevance in our work is that the unaffected knee is very similar to the dislocated knee in adolescents and this should be taken in account in rehabilitation of patients.

Level of evidence

II.     

Comparison of patellofemoral outcomes after TKA using two prostheses with different patellofemoral design features

Purpose

The purpose of the present study was to compare the clinical and radiographic results after TKA using two prostheses with different sagittal patellofemoral design features, including outcomes related to compatibility of the patellofemoral joint.

Methods

The clinical and radiographic results of 81 patients (100 knees) who underwent TKA using the specific prosthesis (group A) were compared with those in a control group who underwent TKA using the other prosthesis (group B). The presence of anterior knee joint pain, patellar crepitation, and patellar clunk syndrome was also checked.

Results

The function score and maximum flexion angle at the last follow-up were slightly better in group A than those in group B (92.0 ± 2.3 vs. 90.6 ± 4.2) (133.6° ± 8.4° vs. 129.6° ± 11.4°). Anterior knee pain was observed in 6 knees and patellar crepitation in four knees in group A. In group B, these symptoms were observed in 22 knees and 18 knees, respectively. There was no patellar clunk syndrome in either group. The alignment was corrected with satisfactory positioning of components. The patellar height remained unchanged after TKA in the two groups. The differences between preoperative and postoperative patellar tilt angle and patellar translation were small.

Conclusion

When comparing the clinical and radiographic results after TKA using two prostheses with different sagittal patellofemoral design features, TKA using the specific prosthesis provided satisfactory results with less clinical symptoms related to the patellofemoral kinematics with TKA using the other prosthesis.

Level of evidence

III.

     

Patellofemoral kinematics during deep knee flexion after total knee replacement: a computational simulation

Purpose

Actions requiring deep knee flexion, such as kneeling and squatting, are challenging to perform after total knee replacement (TKR), though many manufactures emphasize that their knee prostheses could safely achieve high flexion. Little is known about the patellofemoral kinematics during deep flexion. This study aimed to track the movement of the patella during kneeling and squatting through dynamic computational simulation.

Methods

A validated knee model was used to analyse the patellar kinematics after TKR, including shifting, tilting and rotation. The data were captured from full extension to 135° of knee flexion. For kneeling, an anterior force of 500 N was applied perpendicularly on the tibial tubercle as the knee flexed from 90° to 135°. For squatting, a ground reaction force was applied through the tibia from full extension to 135° of flexion.

Results

This study found that patellar shifting and rotation in kneeling were similar to those while squatting. However, during kneeling, the patella had a greater medial tilt and showed signs of abrupt patellar tilt owning to an external force being concentrated on the tibial tubercle.

Conclusions

In terms of squatting and kneeling movements, the latter is a more strenuous action for the patellofemoral joint after TKR due to the high forces acting on the tibial tubercle. It is suggested that overweight patients or those requiring high flexion should try to avoid kneeling to reduce the risk of the polyethylene wear. Further modification of trochlear geometry may be required to accommodate abrupt changes in patellar tilting.

Level of evidence

II.     

The influence of medial patellofemoral ligament on patellofemoral joint kinematics and patellar stability

Purpose

Retinacular restraints have a critical role in patellar tracking, limiting the movement of the patella in the trochlear groove. The medial patellofemoral ligament (MPFL) is probably the main stabilizer against lateral displacement; few studies are focused on MPFL role on patellofemoral kinematics and patellar stability. The main goal of this in vitro study was to analyse the influence of the MPFL on the kinematics of the patellofemoral joint and patellar stability.

Methods

Using a non-image-based navigation system, kinematics and anatomical data of six fresh-frozen specimens were collected. A passive flexion–extension from 0° to 90° and static acquisitions at 0°, 30°, 60° and 90°, with and without 25 N of lateral load, were performed with intact and resected MPFL with a 60 N axial force applied to the isolated quadriceps tendon. Patellar tilt and shift were analysed.

Results

The MPFL intact state showed a shift in medial direction during the first degrees of knee flexion—that disappeared in MPFL resected condition—followed by a lateral shift, similar to that of MPFL resected condition. Tilt analysis showed that patella rotated laterally until 85° of knee flexion for intact MPFL condition and until 70° for resected MPFL condition and after rotated medially. Static tests showed that patellar stability was significantly affected by MPFL resected condition in particular at 30° and 60°.

Conclusions

The MPFL has an aponeurotic nature. It works as a restraint during motion, with an active role under high stress on lateral side, but with a small contribution during neutral knee flexion. Its biomechanical behaviour under loading conditions should be kept into account when performing surgical reconstruction of this ligamentous structure.     

Medial retinacular flap advancement and arthroscopic lateral release for symptomatic chronic patellar lateral subluxation with tilting

Purpose

The purpose of this study was to investigate outcomes of surgical treatment in patients with symptomatic chronic patellar lateral subluxation with tilting.

Methods

Thirty-two patients (38 knees) underwent arthroscopic lateral release and mini-open advancement of medial retinacular flap for the treatment of symptomatic chronic patellar lateral subluxation with tilting with a mean follow-up of 52.0 ± 11.4 months. The mean age at surgery was 24.7 ± 8.8 years, and the duration of symptoms was 4.8 ± 4.1 years. The patellofemoral function of the knee was evaluated before surgery and at the clinical follow-up using the Kujala functional score.

Results

Thirty-six knees (95 %) showed excellent or good results after surgery. Two knees with grade IV chondromalacia of the patella had fair results with persistent apprehension signs and persistent pain. The Kujala patellofemoral functional scores improved by an average of 20.9 points from a mean value of 71.8 ± 12.1 preoperatively to 92.7 ± 10.7 postoperatively (P < 0.01). Radiographically, there were significant improvements in congruence angle from 23.4° ± 7.9° preoperatively to ?7.2° ± 6.4° postoperatively (P < 0.01) and in the lateral patellofemoral angle from ?8.6° ± 6.8° preoperatively to 6.3° ± 4.2° postoperatively (P < 0.01).

Conclusions

Medial retinacular flap advancement and arthroscopic lateral release offer a promising treatment for symptomatic chronic patellar lateral subluxation and tilt without frank traumatic episode.

Level of evidence

Retrospective study, Level IV.     

No difference in patellar tracking between symmetrical and asymmetrical femoral component designs in TKA

Purpose

Poor knee extension function after total knee arthroplasty (TKA) is associated with factors including articular geometry and alignment. Femoral trochlear geometry has evolved from symmetrical to become more prominent proximal–laterally, with the groove aligned proximal–lateral to distal–medial. This study in vitro tested the hypothesis that a modern asymmetrical prosthesis would restore patellar tracking and stability to more natural behaviour than an older symmetrical prosthesis.

Methods

Six knees had their patellar tracking measured optically during active knee extension. Medial–lateral force versus displacement stability was measured at fixed angles of knee flexion. The measurements were repeated after inserting each of the symmetrical and asymmetrical TKAs.

Results

Significant differences of patellar lateral displacement stability, compared to normal, were not found at any angle of knee flexion. The patella tracked medial–laterally within 2.5 mm of the natural path with both TKAs. However, for both TKAs near knee extension, the patella was tilted laterally by approximately 6° and was also flexed approximately 8° more than in the natural knee.

Conclusion

The hypothesis was not supported: The more anatomical component design did not provide more anatomical patellar kinematics and stability.     

Non-anatomical capsular closure of a standard parapatellar knee arthrotomy leads to patellar maltracking and decreased range of motion: a cadaver study

Purpose

A parapatellar approach disrupts the medial soft tissue stabilizers of the patella. We hypothesized that soft tissue realignment during arthrotomy closure of native cadaveric knees influences patellar kinematics leading to decreased range of motion.

Methods

Parapatellar arthrotomy was performed in seven native human cadaveric knees that did not contain arthroplasty components. Capsular closure was performed with figure-of-eight sutures in five different positions for each specimen. The capsule was closed anatomically, and then shifted 1.5 or 3 cm distal, or 1.5 or 3 cm proximal relative to surgical markings of the patellar poles. In each closure position, real-time patellar kinematics and range of motion were recorded using a navigation system with patellar tracking function.

Results

Maximum knee flexion was significantly reduced with closure shifted 3 cm proximal (133° ± 8.2°, p < 0.001) or distal (139° ± 6.4°, p < 0.05) compared to anatomical closure (147° ± 4.1°). All closure positions significantly influenced patellar rotation at 45°, 90°, and 120° of flexion (p < 0.001). Closure 1.5 or 3 cm distal increased lateral patellar shift relative to the mechanical axis (p < 0.01). Patellar tilt was significantly decreased at 90° and 120° by closure 3 cm distal (p < 0.01) and at 120° when closed 1.5 cm distal (p < 0.05).

Conclusions

Imprecise arthrotomy closure significantly impacted patellar kinematics and passive range of motion. Therefore, every effort should be made to provide anatomical closure of the extensor mechanism to preserve native patellar movement kinematics.

Level of evidence

V.     

Sagittal plane tilting deformity of the patellofemoral joint: a new concept in patients with chondromalacia patella

Purpose

The aims of this study were to evaluate sagittal plane alignment in patients with chondromalacia patella via magnetic resonance imaging (MRI), analyse the relationships between the location of the patellar cartilaginous lesions and sagittal alignment and finally investigate the relationships between the sagittal plane malalignment and patellofemoral loadings using by finite element analysis.

Methods

Fifty-one patients who were diagnosed with isolated modified Outerbridge grade 3–4 patellar chondromalacia based on MRI evaluation and 51 control subjects were evaluated. Chondromalacia patella patients were divided into three subgroups according to the chondral lesion location as superior, middle and inferior. The patella–patellar tendon angle (P–PT) was used for evaluation of sagittal alignment of patellofemoral joint. Each subgroup was compared with control group by using P–PT angle. To investigate the biomechanical effects of sagittal plane malpositioning on patellofemoral joint, bone models were created at 30°, 60° and 90° knee flexion by using mean P–PT angles, which obtained from patients with chondromalacia patellae and control subjects. The total loading and contact area values of the patellofemoral joints were investigated by finite element analysis.

Results

The mean age of all participants was 52.9 ± 8.2 years. The mean P–PT angle was significantly lower in chondromalacia group (142.1° ± 3.6°) compared to control group (144.5° ± 5.3°) (p = 0.008). Chondral lesions were located in superior, middle and inferior zones in 16, 20 and 15 patients, respectively. The mean P–PT angles in patients with superior (141.8 ± 2.7) and inferior subgroups (139.2 ± 2.3) were significantly lower than the values in the control group (p < 0.05). The contact area values were detected higher in models with chondromalacia than in the control models at the same flexion degrees. There were increased loadings at 30° and 90° flexions in the sagittal patellar tilt models.

Conclusion

This study revealed that sagittal plain malpositioning of the patellofemoral joint might be related to chondromalacia, especially in the presence of lesions in the upper and lower part of the patella. This condition leads to supraphysiological loadings on the patellofemoral joint. Sagittal patellar tilt should be considered in the evaluation and management of patellar cartilage defects. Taking sagittal plane malalignment into consideration in patellofemoral joint evaluation will enable us to design new physical and surgical modalities.

Level of evidence

IV.

     

Prevalence and clinical significance of chondromalacia isolated to the anterior margin of the lateral femoral condyle as a component of patellofemoral disease: observations at MR imaging

Objective

To determine the prevalence of chondromalacia isolated to the anterior margin of the lateral femoral condyle as a component of patellofemoral disease in patients with anterior knee pain and to correlate it with patient demographics, patellar shape, and patellofemoral alignment.

Materials and methods

Retrospective study over a 1-year period reviewing the MR knee examinations of all patients who were referred for assessment of anterior knee pain. Only patients with isolated lateral patellofemoral disease were included. Age, gender, distribution of lateral patellofemoral chondromalacia, and grade of cartilaginous defects were documented for each patient. Correlation between the distribution of lateral patellofemoral chondromalacia and patient demographics, patellar shape, and indices of patellar alignment (femoral sulcus angle and modified Q angle) was then ascertained.

Results

There were 50 patients (22 males, 28 females) with anterior knee pain and isolated patellofemoral disease. The majority of the patients (78 %) had co-existent disease with grade 1 chondromalacia. No significant correlation was found between patients with chondromalacia isolated to the anterior margin of the lateral femoral condyle and age, gender, patellar shape, or modified Q angle (p?>?0.05). However, patients with chondromalacia isolated to the anterior margin of the lateral femoral condyle had a shallower femoral sulcus angle (mean 141.8°) compared to the patients with lateral patellar facet disease (mean 133.8°) (p?=?0.002).

Conclusions

A small percentage of patients with anterior knee pain have chondromalacia isolated to the anterior margin of the lateral femoral condyle. This was associated with a shallower femoral sulcus angle.