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.     

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.     

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.     

Radiographic landmarks for tunnel placement in reconstruction of the medial patellofemoral ligament

Purpose

To verify the findings of previous studies in confirming radiographic landmarks for the femoral attachment of the medial patellofemoral ligament (MPFL), but also to define radiographic landmarks for the patellar attachment. Assess the effect of limb rotation upon these radiographic landmarks.

Methods

The medial patellofemoral ligament was identified in ten fresh-frozen human cadaveric knees. A headed pin was used to mark the centre of the femoral and patellar attachments. True lateral radiographs were performed followed by lateral radiographs in 10° and 20° of internal and external rotation. Posterior-anterior and proximal?Cdistal position of the headed pin was evaluated.

Results

The femoral attachment averaged 3.8?±?5.0?mm anterior to the posterior femoral cortical line and 0.9?±?2.4?mm distal to the perpendicular line intersecting the posterior aspect of Blumensaat??s line. The patellar attachment averaged 7.4?±?3.5?mm anterior to the posterior patellar cortical line, 5.4?±?2.6?mm distal to the perpendicular line intersecting the proximal margin of the patellar articular surface. There was a significant relationship between limb rotation and distance of femoral and patellar attachment from the posterior cortical line (P?<?0.0001 and P?<?0.0002 respectively).

Conclusion

Radiographic landmarks for the femoral attachment of the MPFL identified in this study are comparable with other recent work. This study describes new radiographic landmarks for the patellar attachment of the MPFL and highlights that it is essential to acquire true lateral radiographs if these radiographic landmarks are to be interpreted accurately.     

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.     

Anatomic medial patellofemoral ligament reconstruction using patellar suture anchor fixation for recurrent patellar instability

Purpose

The purpose of this study was to prospectively evaluate clinical and radiographic outcomes following anatomic medial patellofemoral ligament (MPFL) reconstruction using patellar suture anchor fixation for recurrent patellar instability.

Methods

Twenty patients (20 knees) were enrolled in this study. The median age was 21 years, and the median follow-up was 34.5 months. Reconstruction was performed using a hamstring autograft fixed with two suture anchors at native patellar site of the MPFL. No patient had undergone additional medial tibial tuberosity transfer. Clinical scores (Kujala, Lysholm, and Tegner score) and apprehension test were completed preoperatively and at the follow-up. Preoperative and follow-up radiographic assessments included modified Insall-Salvati ratio, congruence angle, and lateral patellofemoral angle.

Results

The preoperative Kujala and Lysholm scores were 52.6 ± 12.4 and 49.2 ± 10.7, and at follow-up visits, corresponding values were 90.9 ± 4.5 (p < 0.001) and 90.9 ± 5.2 (p < 0.001). Tegner score increased from 3.0 (range 1–4) to 5.0 (range 4–7) (p < 0.001). The apprehension test was positive in all patients preoperatively, but only positive in one patient at follow-up. All radiographic assessments were significantly improved; modified Insall-Salvati index (from 1.75 to 1.65) (p = 0.002), congruence angle (from 6.3° to ?7.0°) (p < 0.001), and lateral patellofemoral angle (from 2.1° to 4.9°) (p = 0.008). No patient experienced a patellar fracture or redislocation.

Conclusion

These results are comparable to those of bone tunnel techniques reported in the literature. This study shows that anatomic MPFL reconstruction using two suture anchors is a reliable treatment option.

Level of evidence

Case series with no comparison group, Level IV.     

Lateral retinaculum plasty instead of lateral retinacular release with concomitant medial patellofemoral ligament reconstruction can achieve better results for patellar dislocation

Purpose

To elucidate the outcomes of lateral retinaculum plasty versus lateral retinacular release with concomitant medial patellofemoral ligament (MPFL) reconstruction.

Methods

In a prospective study, 59 patients treated at our institution from 2012 to 2014 were included. The 59 patients were randomly divided into two groups. Group I included 27 patients who underwent lateral retinacular release and MPFL reconstruction. Group II included 32 patients who underwent lateral retinaculum plasty and MPFL reconstruction. All patients were followed up for at least 2 years and all assessments were performed both pre- and post-operation. Clinical evaluation consisted of the Kujala score, patellar medial glide test, and patellar tilt angle, patellar lateral shift, and congruence angle, measured on CT scan.

Results

Significant improvement was seen after surgery in both groups. The group of lateral retinaculum plasty achieved better results than the group of lateral retinacular release. No statistically significant differences were found in lateral patellar shift (ns) or congruence angle (ns) between the groups. There were significant differences in Kujala score (P?<?0.05) patellar tilt angle (P?<?0.05), and patellar medial glide test (P?<?0.05) between the groups.

Conclusions

MPFL reconstruction with lateral retinaculum plasty yielded better results than MPFL with lateral retinacular release. Postoperatively, medial and lateral function were restored, and patellar tracking was normal. Lateral retinaculum plasty is a new method that reduces the complications of lateral retinacular release for patellar dislocation.

Level of evidence

II.

     

Anatomical factors influencing patellar tracking in the unstable patellofemoral joint

Purpose

The current study was performed to relate anatomical parameters to in vivo patellar tracking for pediatric patients with recurrent patellar instability.

Methods

Seven pediatric patients with recurrent patellar instability that failed conservative treatment were evaluated using computational reconstruction of in vivo patellofemoral function. Computational models were created from high-resolution MRI scans of the unloaded knee and lower-resolution scans during isometric knee extension at multiple flexion angles. Shape matching techniques were applied to replace the low-resolution models of the loaded knee with the high-resolution models. Patellar tracking was characterized by the bisect offset index (lateral shift) and lateral tilt. Anatomical parameters were characterized by the inclination of the lateral ridge of the trochlear groove, the tibial tuberosity–trochlear groove distance, the Insall–Salvati index and the Caton–Deschamps index. Stepwise multivariable linear regression analysis was used to relate patellar tracking to the anatomical parameters.

Results

The bisect offset index and lateral tilt were significantly correlated with the lateral trochlear inclination (p ≤ 0.002) and TT–TG distance (p < 0.05), but not the Insall–Salvati index or the Caton–Deschamps index. For both the bisect offset index and lateral tilt, the standardized beta coefficient, used to identify the best anatomical predictors of tracking, was larger for the lateral trochlear inclination than the TT–TG distance.

Conclusion

For this population, the strongest predictor of lateral maltracking that could lead to patellar instability was lateral trochlear inclination.

Level of evidence

Diagnostic study, Level II.     

Lateral release and medial plication for recurrent patella dislocation

Purpose

This study aims to report the long-term results of lateral release and medial plication in patients with recurrent patellar dislocation.

Methods

In this study, 31 patients who underwent surgery for recurrent patellar dislocation were retrospectively reviewed between 1994 and 2004. Among the 31 patients were 12 male and 19 female patients. The average age was 23.9?±?4.8?years, and the mean follow-up period was 11.6?±?2.4?years.

Results

Three patients had postoperative dislocations. The mean Kujala score significantly improved from 57.5?±?13.2 points preoperatively to 89.2?±?8.7 points at the final follow-up (P?<?0.0001). The median Tegner activity score significantly improved from 3 (range, 1?C5) at preoperative examination to 7 (range, 3?C9) at the final follow-up (P?<?0.0001). Ten patients were rated as excellent, 18 as good, 2 as fair, and 1 as poor. The congruence angle improved from 16.5°?±?3.0° to ?2.8°?±?2.7°, and the lateral patellofemoral angle improved from ?4.2°?±?1.9° to 8.2°?±?2.5°. There was no case of osteoarthritis at the final follow-up.

Conclusions

Percutaneous lateral release and medial plication showed satisfactory results with limited morbidity in the long-term follow-up. This traditional method remains a simple and effective surgical procedure for recurrent patellar dislocation.

Level of evidence

Therapeutic, Level IV.     

Assessment of in vivo loading history of the patellofemoral joint: a study combining patellar position,tilt, alignment and bone SPECT/CT

Purpose

The current study investigates whether patella height and tilt or leg alignment influence the intensity values as well as the distribution pattern of single photon emission computerized tomography/computerized tomography (SPECT/CT) tracer uptake in the patellofemoral joint.

Methods

99mTc-HDP-SPECT/CT and radiographs of consecutive 84 knees were prospectively obtained. Lateral radiographs were analyzed in terms of patellar height, Insall-Salvati index and modified Insall-Salvati index. Skyline views were analyzed for Laurin’s lateral patellofemoral angle. On long-leg radiographs, the mechanical leg alignment was classified as varus, valgus or neutral. SPECT/CT was analyzed for each anatomical region using a previously validated SPECT/CT localization and grading algorithm. Mean, standard deviation, minimum and maximum of grading for each area of the localization scheme were recorded. Nonparametric Spearman’s correlations were used to correlate patellar height, lateral patellar angle and leg alignment with the tracer uptake intensity. Chi-square statistics were used for categorical data (p < 0.05).

Results

A patella baja correlated significantly with higher SPECT/CT tracer uptake in all patellar and lateral femoral regions (p < 0.001). A higher lateral patellar tilt correlated significantly with higher tracer uptake in the superior lateral femoral parts and the tibial tubercle. In mechanically varus aligned knees, there was significantly higher SPECT/CT tracer uptake on the medial and in valgus knees on the lateral part of the patellofemoral joint (p < 0.05).

Conclusions

As the intensity and distribution of the SPECT/CT significantly correlated with patella baja and patellar tilt, SPECT/CT might be considered as imaging modality for evaluating patients with patellofemoral disorders and for follow-up of patients after patellofemoral realignment procedures.

Level of evidence

Diagnostic study, Level II.     

Minimum joint space width (mJSW) of patellofemoral joint on standing “skyline” radiographs: test-retest reproducibility and comparison with quantitative magnetic resonance imaging (qMRI)

Objective

To assess the intraobserver, interobserver, and test-retest reproducibility of minimum joint space width (mJSW) measurement of medial and lateral patellofemoral joints on standing “skyline” radiographs and to compare the mJSW of the patellofemoral joint to the mean cartilage thickness calculated by quantitative magnetic resonance imaging (qMRI).

Materials and methods

A couple of standing “skyline” radiographs of the patellofemoral joints and MRI of 55 knees of 28 volunteers (18 females, ten males, mean age, 48.5?±?16.2 years) were obtained on the same day. The mJSW of the patellofemoral joint was manually measured and Kellgren and Lawrence grade (KLG) was independently assessed by two observers. The mJSW was compared to the mean cartilage thickness of patellofemoral joint calculated by qMRI.

Results

mJSW of the medial and lateral patellofemoral joint showed an excellent intraobserver agreement (interclass correlation (ICC)?=?0.94 and 0.96), interobserver agreement (ICC?=?0.90 and 0.95) and test-retest agreement (ICC?=?0.92 and 0.96). The mJSW measured on radiographs was correlated to mean cartilage thickness calculated by qMRI (r?=?0.71, p?<?0.0001 for the medial PFJ and r?=?0.81, p?<?0.0001 for the lateral PFJ). However, there was a lack of concordance between radiographs and qMRI for extreme values of joint width and KLG. Radiographs yielded higher joint space measures than qMRI in knees with a normal joint space, while qMRI yielded higher joint space measures than radiographs in knees with joint space narrowing and higher KLG.

Conclusions

Standing “skyline” radiographs are a reproducible tool for measuring the mJSW of the patellofemoral joint. The mJSW of the patellofemoral joint on radiographs are correlated with, but not concordant with, qMRI measurements.     

The association of infrapatellar fat pad oedema with patellar maltracking: a case–control study

Objective

To look for any association between oedema in the superolateral portion of the infrapatellar fat pad and patellar maltracking.

Materials and methods

We compared two groups of knee MRI with regard to five patellar maltracking parameters. The first group included 100 knees with evidence of oedema in the superolateral aspect of the infrapatellar fat pad (the study group). The second group included another 100 knee MRI that had a normal infrapatellar fat pad (the control group). The five patellar maltracking parameters assessed were the trochlear depth, tibial tuberosity–trochlear groove distance (TTTG), patellar translation, patellofemoral angle (PFA) and the Insall–Salvati index.

Results

There was a statistically significant difference in the Insall–Salvati index, patellar translation and PFA between the two groups (p value of <0.001, <0.001 and 0.004 respectively, Student’s t test). There was a higher prevalence of patella alta, lateral patellar displacement (LPD) and lateral patellar tilt in the study group (p value of <0.001, <0.001 and 0.011 respectively, Fisher’s exact test). Sixty out of 100 knees in the study group had at least one abnormal patellar maltracking parameter in comparison to 16 out of 100 knees in the control group (p?Conclusion Oedema in the superolateral portion of Hoffa’s fat pad, the MRI feature of fat pad impingement, is associated with patellar maltracking.     

Treatment of isolated patellofemoral osteoarthritis with lateral facetectomy plus Insall’s realignment procedure: long-term follow-up

Purpose

To assess the long-term results of lateral facetectomy plus Insall’s realignment procedure to treat isolated patellofemoral osteoarthritis.

Methods

All consecutive patients undergoing this procedure with a follow-up between 10 and 14 years were included in this study. Subjects were excluded if they had previous patellar dislocation, patellar fracture, tibiofemoral osteoarthritis (except mild cases) or follow-up <10 or >14 years. Failure cases (need for total knee arthroplasty) of this surgical procedure before 10 years of follow-up were considered in the overall failure rate. Clinical, functional and radiographic outcomes were obtained at baseline and compared to postoperative values.

Results

Forty-three patients (mean (SD) age 59.7 (8.1) years) had a follow-up between 10 and 14 years and were finally included in this study. The failure rate in the whole series and included patients was 26.4 and 16.3 %, respectively, for a mean (SD) follow-up of 9.2 (3.2) years and 11.7 (1.4) years, respectively. Patellofemoral pain (p < 0.0001), need for NSAIDs (p < 0.0001), longitudinal (p < 0.0001) and transversal (p < 0.0001) patellar glide tests, Zholen’s sign (p = 0.0007) and knee effusion (p = 0.02) significantly improved in the follow-up. Postoperative Knee Society Score (KSS) anatomical (p < 0.0001), functional (p < 0.0001) and total (p < 0.0001) scores and Kujala’s score (p = 0.001) were significantly higher compared to preoperative values. The patellar tilt (p = 0.001) and shift (p = 0.04) significantly improved postoperatively, whereas the patellofemoral osteoarthritis was not modified (n.s.) with respect to preoperative assessment.

Conclusions

The lateral facetectomy plus Insall’s realignment procedure was a successful treatment for isolated patellofemoral osteoarthritis from a clinical, functional and radiographic point of view in the long-term follow-up.

Level of evidence

Prospective case series, Level IV.     

Cine MR imaging before and after realignment surgery for patellar maltracking — comparison with axial radiographs

Objective Comparison of motion-triggered cine magnetic resonance (MR) imaging and conventional radiographs for the assessment of operative results of patellar realignment.Subjects and methods Fifteen patients with recurrent patellar dislocation or patellar subluxation were evaluated with conventional axial radiographs before and after realignment surgery by measuring the congruence angle (CA), lateral patellofemoral angle (LPFA), and lateral displacement (d). In eight patients the patellofemoral joint was additionally evaluated pre- and postoperatively with motion-triggered cine MR imaging by determining the bisect offset (BSO), lateral patellar displacement (LPD), and patellar tilt angle (PTA).Results and conclusions Significant differences between the pre- and postoperative measurements were found for all MR imaging parameters (BSO, LPD, PTA: p<0.01) but not for the conventional X-ray parameters (CA: p=0.70, LPFA: p=0.56; d: p=0.04). Motion-triggered cine MR imaging was superior to conventional tangential radiographs for assessing the effectiveness of patellar realignment surgery.     

Shear wave elastography properties of vastus lateralis and vastus medialis obliquus muscles in normal subjects and female patients with patellofemoral pain syndrome

Objective

The aim of our study was to define and compare the mechanical properties of the vastus lateralis (VL) and vastus medialis obliquus muscles (VMO) by the way of quantitative shear-wave elastography in male and female healthy control (HC) subjects, and in female patients with patellofemoral pain syndrome (PFPS).

Materials and methods

Twenty-two healthy volunteers (11 male and 11 female) and 11 female patients with anterior knee pain were included in the study. The SWE examinations for VL and VMO were performed while the subjects were performing open kinetic chain exercises in neutral and 30° hip abduction. The contraction capacity (CC) and contraction ratio (CR) values were determined in resting and contraction phases in both hip positions.

Results

The mean elasticity values in the CC for VL and VMO muscles were significantly higher in male HC subjects when compared to female HC subjects (p?<?0.05). The CR of the VL muscle in female patients with PFPS was not significantly different than the female HC group. The CR for the VMO muscle was significantly lower in female patients with PFPS when compared to female HC subjects (p?<?0.05).

Conclusions

We found a significant VMO weakness, and this method may provide quantitative data that might influence the diagnosis of muscle weakness, in female patients with PFPS.     

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.     

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.     

Magnetic resonance imaging of patellofemoral relationships

Patellofemoral relationships were analyzed in 11 patients (13 knees) with patellar dislocation and 15 asymptomatic subjects (15 knees) at 0° and 20° of flexion. The measurements were made from five consecutive axial images through the patellofemoral joint. The six indices measured were lateral patellar tilt (LPT), lateral patellofemoral angle (LPA), lateral patellar displacement (LPD), patella-lateral condyle index (L/PW), congruence angle (CA), and sulcus angle (SA). The reproducibility of the method was evaluated. The difference between the two study groups was more evident at 0° than at 20° of knee flexion. Significant differences were noted between measurements made at different levels of the joint, particularly in the controls. Isometric contraction of the quadriceps muscle lateralized and tilted the patella slightly in both groups. L/PW with and without quadriceps muscle contraction, and LPA with reference to the anterior condyles differentiated between the two study groups most clearly. LPT and LPA with reference to the anterior condyles differentiated the study groups better than LPT and LPA with reference to the posterior condyles. The reproducibility was good except for inter-observer comparison of CA and SA. The use of an imaging plane selected at the midpoint of the patellar articular cartilage increases the sensitivity of the measurements, since it takes into account both the height of the patella and the tendency towards lateralization. These results indicate that patellar tilt is best measured with the LPA index and patellar lateralization with the L/PW index at 0° knee flexion. This study should always include isometric contraction of the quadriceps muscle.     

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.     

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.