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.     

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.     

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.     

Increased patellofemoral pressure after TKA: an in vitro study

Purpose

Considering the discrepant results of the recent biomechanical studies, the purpose of this study was to simulate dynamic muscle-loaded knee flexion with a large number of specimens and to analyse the influence of total knee arthroplasty (TKA) without and with patellar resurfacing on the patellofemoral pressure distribution.

Methods

In 22 cadaver knee specimens, dynamic muscle-loaded knee flexion (15°–90°) was simulated with a specially developed knee simulator applying variable muscle forces on the quadriceps muscles to maintain a constant ankle force. Patellofemoral pressures were measured with flexible, pressure-sensitive sensor foils (TEKSCAN) and patellofemoral offset with an ultrasound motion-tracking system (ZEBRIS). Measurements were taken on the native knee, after total knee arthroplasty and after patellar resurfacing. Correct positioning of the patellar implant was examined radiologically.

Results

The maximal patellofemoral peak pressure partly increased from the native knee to the knee with TKA with intact patella (35°–90°, p < 0.012) and highly increased (twofold to threefold) after patellar resurfacing (20°–90°, p < 0.001). Concurrently, the patellofemoral contact area decreased and changed from a wide area distribution in the native knee, to a punctate area after TKA with intact patella and a line-shaped area after patellar resurfacing. Patellar resurfacing led to no increase in patellar thickness and patellofemoral offset.

Conclusions

Despite correct implantation of the patellar implants and largely unchanged patellofemoral offset, a highly significant increase in pressure after patellar resurfacing was measured. Therefore, from a biomechanical point of view, the preservation of the native patella seems reasonable if there is no higher grade patellar cartilage damage.     

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.     

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.     

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.     

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.     

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.     

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.     

In vitro measurement of patellar kinematics following reconstruction of the medial patellofemoral ligament

This study compares the effects of two different techniques of medial patellofemoral ligament (MPFL) reconstruction, and proximal soft tissue realignment on patellar stabilization against lateral dislocation. Eight human cadaver knee specimens with no radiological pathomorpholgy on a straight lateral view, contributing to patellofemoral instability, were mounted in a kinematic knee simulator and isokinetic extension was simulated. Patellar kinematics were measured with an ultrasound positioning system (zebris^®) while a 100 N laterally directed force was applied to the patella. The kinematics were compared with intact knee conditions under MPFL deficient conditions, as well as following dynamic reconstruction of the MPFL using a distal transfer of the semitendinosus tendon, following static reconstruction by a semitendinosus autograft, and following proximal soft tissue realignment of the patella (Insall procedure). Dynamic reconstruction of the MPFL resulted in no significant alteration (P = 0.16) of patellar kinematics. Static reconstruction of the MPFL significantly medialized (P < 0.01) the patellar movement without, but restored intact knee kinematics under the laterally directed force. In contrast, following proximal soft tissue realignment, the patellar movement was constantly medialized and internally tilted (P = 0.04). Dynamic and static reconstruction of the MPFL create sufficient stabilization of the patella. Following proximal soft tissue realignment, the patellar position was over-medialized relative to intact knee conditions, which could lead to an overuse of the medial retropatellar cartilage.     

Variations in kinematics and function following patellar stabilization including tibial tuberosity realignment

Purpose

The current study was performed to characterize the influence of patellar stabilization procedures on patellofemoral and tibiofemoral dynamic motion.

Methods

Six knees were evaluated pre-operatively and 1 year or longer following stabilization via tibial tuberosity realignment, with simultaneous medial patellofemoral ligament reconstruction performed for five knees. Knees were imaged during extension against gravity using a dynamic CT scanner. Models representing each knee at several positions of extension were reconstructed from the images. Local coordinate systems were created within one femur, patella and tibia for each knee, with shape matching of the bones used to transfer the coordinate axes to the other models. The patellar lateral shift and tilt and tibial external rotation were quantified based on the reference axes and interpolated to flexion angles from 5° to 40°. Pre-operative and post-operative data were compared with the paired t tests.

Results

Surgical realignment significantly decreased the average patellar lateral shift and tilt at low flexion angles. At 5°, surgical realignment decreased the average lateral shift from 15.5 (6.3) to 8.5 (4.7) mm and decreased the average lateral tilt from 20.8 (9.4)° to 13.8 (6.4)°. The changes were statistically significant (p < 0.05) at 5° and 10° of flexion, as well as 20° for lateral shift. The average tibial external rotation also increased significantly at 30° and 40° following surgery.

Conclusion

Patellar stabilization including a component of tuberosity realignment reduces patellar lateral shift and tilt at low flexion angles, but the long-term influence of increased tibial external rotation on tibiofemoral function is currently unknown.

Level of evidence

Prospective comparative study, Level II.     

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.     

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.     

Dynamic measurement of patellofemoral kinematics and contact pressure after lateral retinacular release: an in vitro study

The purpose of this study was to investigate the influence of lateral retinacular release and medial and lateral retinacular deficiency on patellofemoral position and retropatellar contact pressure. Human knee specimens (n = 8, mean age = 65 SD 7 years, all male) were tested in a kinematic knee-simulating machine. During simulation of an isokinetic knee extension cycle from 120° to full extension, a hydraulic cylinder applied sufficient force to the quadriceps tendon to produce an extension moment of 31 Nm. The position of the patella was measured using an ultrasound based motion analysis system (CMS 100^®, Zebris). The amount of patellofemoral contact pressure and its pressure distribution was measured using a pressure sensitive film (Tekscan^®, Boston). Patellar position and contact pressure were first investigated in intact knee conditions, after a lateral retinacular release and a release of the medial and lateral retinaculum. After lateral retinacular release the patella continuously moved from a significant medialised position at flexion (P = 0.01) to a lateralised position (P = 0.02) at full knee extension compared to intact conditions, the centre of patellofemoral contact pressure was significantly medialised (0.04) between 120° and 60° knee flexion. Patellofemoral contact pressure did not change significantly. In the deficient knee conditions the patella moved on a significant lateralised track (P = 0.04) through the entire extension cycle with a lateralised centre of patellofemoral pressure (P = 0.04) with a trend (P = 0.08) towards increased patellofemoral pressure. The results suggest that lateral retinacular release did not inevitably stabilise or medialise patellar tracking through the entire knee extension cycle, but could decrease pressure on the lateral patellar facet in knee flexion. Therefore lateral retinacular release should be considered carefully in cases of patellar instability.     

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.

     

Allowing one quadrant of patellar lateral translation during medial patellofemoral ligament reconstruction successfully limits maltracking without overconstraining the patella

Purpose

Graft tensioning during medial patellofemoral ligament (MPFL) reconstruction typically allows for lateral patellar translation within the trochlear groove. Computational simulation was performed to relate the allowed patellar translation to patellofemoral kinematics and contact pressures.

Methods

Multibody dynamic simulation models were developed to represent nine knees with patellar instability. Dual limb squatting was simulated representing the pre-operative condition and simulated MPFL reconstruction. The graft was tensioned to allow 10, 5, and 0 mm of patellar lateral translation at 30° of knee flexion. The patellofemoral contact pressure distribution was quantified using discrete element analysis.

Results

For the 5 and 10 mm conditions, patellar lateral shift decreased significantly at 0° and 20°. The 0 mm condition significantly decreased lateral shift for nearly all flexion angles. All graft conditions significantly decreased lateral tilt at 0°, with additional significant decreases for the 5 and 0 mm conditions. The 0 mm condition significantly increased the maximum medial pressure at multiple flexion angles, increasing by 57% at 30°, but did not alter the maximum lateral pressure.

Conclusions

Allowing 5 to 10 mm of patellar lateral translation limits lateral maltracking, thereby decreasing the risk of post-operative recurrent instability. Allowing no patellar translation during graft tensioning reduces maltracking further, but can overconstrain the patella, increasing the pressure applied to medial patellar cartilage already fibrillated or eroded from an instability episode.

     

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.     

The patellofemoral kinematics in patients with untreated developmental dislocation of the hip suffering from patellofemoral pain

Purpose

This study reviews the dynamic patellofemoral CT results of 39 patients with untreated developmental dislocation of the hip who are suffering from knee pain.

Method

The mean age of the patients with unilateral developmental dislocation of the hip was 33.3 (±7.9), for bilateral patients 36.2 (±11.3), and for the control group, it was 31.5 (±8.5). While 14 of them were bilateral, 25 were unilateral. The CT results of 24 asymptomatic adult knees served as the control group. The patellofemoral parameters of patients with unilateral and bilateral developmental dislocation of the hip, the control group’s parameters and the effect of femoral anteversion, limb length discrepancy, severity of dislocation, the mechanical axis deviation on patellofemoral parameters were analyzed.

Results

In patients with unilateral untreated developmental dislocation of the hip, although the patella was located more laterally at initial flexion degrees, it was located more medially at 30° and 60° flexion with respect to the control group. For the involved extremity, the PTA angles at 15°, 30°, and 60° flexion were significantly higher than in the control group corresponding to medial patellar tilt. In patients with bilateral developmental dislocation of the hip, the course of the patella during tracking in terms of patellar shift was similar to that of the unilateral patients. The amount of leg length discrepancy and the severity of dislocation, as well as the mechanical axis deviation, did not affect the patellofemoral parameters.

Conclusion

The patients with untreated developmental dislocation of the hip and suffering from knee pain should be analyzed not only for tibiofemoral abnormalities but also for patellofemoral malalignment.

Level of evidence

Case–control study, Level III.     

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.