Lateral patellar maltracking due to trochlear dysplasia: A computational study

BackgroundThe study focuses on the influence of trochlear dysplasia on patellar tracking related to patellar instability.MethodsKnee extension against gravity and dual-limb squatting were simulated with seven models representing knees being treated for recurrent instability. Trochlear depth was altered to represent lateral trochlear inclination (LTI) values of 6°, 12° and 24°. Repeated measures analyses compared patellar lateral shift (bisect offset index) across different LTI values. Peak bisect offset index during extension and squatting was correlated with patella alta (Caton–Deschamps index) and maximum lateral position of the tibial tuberosity.ResultsBisect offset index varied significantly (p < 0.05) between different LTI values at multiple flexion angles throughout simulated knee extension and squatting. Average bisect offset values were 1.02, 0.95, and 0.86 for LTI = 6°, 12°, and 24°, respectively, at 0° of flexion for knee extension. The strongest correlation occurred between peak bisect offset index and lateral position of the tibial tuberosity for knee squatting with LTI = 6° (r² = 0.81, p = 0.006). The strength of the correlation decreased as LTI increased. Caton–Deschamps was only significantly correlated with patellar tracking for LTI = 24° during knee squatting.ConclusionsA shallow trochlear groove increases lateral patellar maltracking. A lateral tibial tuberosity in combination with trochlear dysplasia increases lateral patellar tracking and the risk of patellar instability. Patella alta has relatively little influence on patellar tracking in combination with trochlear dysplasia due to the limited articular constraint provided by the trochlear groove.     

Comparisons of patellar bone mineral density between individuals with and without patellofemoral pain

BackgroundAlthough bone stress injuries have been reported in individuals with patellofemoral pain (PFP), especially within the lateral patella, it remains unclear whether persons with PFP exhibit altered patellar regional bone mineral density (BMD). The primary purpose of this study was to compare BMD of the patella (lateral, medial, and total regions) between individuals with and without PFP using quantitative computed tomography (QCT). The secondary aim was to examine the associations between patellar regional BMD and patellofemoral joint (PFJ) alignment.MethodsTen individuals with retropatellar pain and 10 sex, age, weight, height, and activity matched pain-free controls underwent a QCT scan to obtain patellar BMD. To quantify PFJ alignment, patellar lateral displacement was measured using bisect-offset (BSO) index and patellar mediolateral tilt was quantified using patellar tilt angle (PTA). A two-factor repeated-measures ANOVA was used to compare BMD across the three patellar regions and between the two groups. Pearson correlation coefficient analyses were used to evaluate the associations between BMD and PFJ alignment of all participants.ResultsThere was no difference in BMD between the two groups. However, BMD was highest within the lateral patella and was lowest within the medial patella across both groups. There were significantly moderate to large correlations between BSO index/PTA and BMD within lateral, medial, and total regions.ConclusionsWhile individuals with PFP and pain-free controls have similar patellar BMD, the lateral patella exhibits the highest BMD. Additionally, higher patellar regional BMD is related to increased patellar lateral displacement and lateral tilt.     

Femoral trochlear dysplasia after patellar dislocation in rabbits

BackgroundThe aim of this study was to investigate the effects of patellar dislocation on the development of the trochlear groove in rabbits.MethodsEighty knees from forty one-month-old white rabbits were divided into three groups (sham surgery, experimental, control). Lateral patellar dislocation was established in the experimental group and the effect on the development of the trochlear groove was compared with that in the sham surgery and control groups. Computed tomography (CT) scans were conducted to measure the angle, width and depth of the trochlear groove one month and six months after surgery. Gross specimen examination, cross-sectional anatomy and histological observation were conducted to investigate the anatomical configuration of the femoral trochlea and the changes in cartilage tissue of the trochlear groove at six months after surgery.ResultsAt six months after surgery, CT scans showed a significant difference between the sham surgery group and the experimental group in the angle, width and depth of the trochlear groove. There were no significant differences between the sham surgery group and the control group. Gross specimen examination and cross-sectional anatomy indicated low lateral femoral trochlea and reduced height at the trochlear groove in the experimental group. The femoral trochlea was of normal appearance in the other two groups. Histological investigations showed that there were degenerative changes in the cartilage tissue of the femoral trochlea in the experimental group.ConclusionsSecondary femoral trochlear dysplasia may be caused by patellar dislocation in a normally developing femoral trochlea. Patellar dislocation may be one of the causes of femoral trochlear dysplasia.     

The effect of biplane medial opening wedge high tibial osteotomy on patellofemoral joint indices

PurposeThis study was designed to examine the effect of biplane medial opening wedge high tibial osteotomy (MOWHTO) on patellofemoral indices and posterior tibial slope.Materials and methodsSixty-two knees (61 patients) underwent biplane MOWHTO for unicompartmental osteoarthritis of the knee. Patellar indices were measured by radiographic assessment postoperatively. The Merchant's views were used for patellar tilt and shift while standing lateral view radiographs were used for the patellar height analysis using the modified Blackburne-peel ratio (mBP). The patients were divided into two groups according to the change between the pre- and postoperative mechanical axis. Group A constituted the correction angle of equal more than 10°, and group B of less than 10°.ResultsGroup A demonstrated a significant change of mechanical axis and the tibial slope. Patellar indices including the patellar tilt, shift, and mBP did not show significant difference. Group B demonstrated the statistical significant difference in only the mechanical axis deviation. Patellar indices including the patellar tilt, shift, and mBP as well as the tibia slope did not show significant difference. When evaluated as a whole group, the mean shift in weight bearing line, patellar height (mBP), and tibial slope from preoperative to postoperative value was statistically significant. However, the patellar tilt and shift were not changed significantly.ConclusionsAfter biplane MOWHTO, patellar tilt and shift do not significantly change when measured on static mode supine X-ray. However, patella was lowered and tibia slope increased after MOWHTO.Level of evidenceII.     

Effect of Q-angle on patellar positioning and thickness of knee articular cartilages

The purpose of the present study was to investigate whether an increased quadriceps angle (Q-angle) has an effect on patellar positioning and/or the thickness of the medial and lateral tibiofemoral and patellofemoral articular cartilage and menisci, in a group of young asymptomatic individuals. These individuals were detected in a previous study with a decreased anatomical cross-sectional area of the vastus medialis and lateralis as a result of an increased Q-angle. Patellar positioning and the thickness of the articular cartilages were determined in 19 asymptomatic male individuals with high Q-angle (HQ-angle) (18.5° ± 2.6°) using magnetic resonance imaging (MRI). Seventeen male counterparts with low Q-angle (10.1° ± 1.9°) were used for comparison. The position of the patella was determined by measuring the sulcus angle, the lateral patella tilt, the patella-lateral condyle index and the bisect offset (BSO) with the quadriceps relaxed. The BSO, was also measured with the quadriceps under maximum isometric voluntary contraction. The thickness of the articular cartilages of the lateral and medial femoral condyles, the tibial condyles, the patellar facets and the menisci were also measured. Our data revealed that healthy individuals with HQ-angle are unlikely to demonstrate any changes in the position of the patella and/or the thickness of the knee articular cartilages. The decreased anatomical area of the vastus medialis and an almost equally atrophied vastus lateralis, which was previously observed in this group of individuals may prevent in part the misalignment of the patella and early wear of the tibiofemoral and patellofemoral articular cartilages.     

Lateral retinacular release in concordance with medial patellofemoral ligament reconstruction in patients with recurrent patellar instability: A computational model

BackgroundThe aim of this study was to develop and validate a finite element (FE) model of the patellofemoral joint to analyze the biomechanics of lateral retinacular release after medial patellofemoral ligament (MPFL) reconstruction in patellar malalignment (increased tibial tubercle–trochlear groove distance (TT-TG)). We hypothesized that lateral retinacular release is not appropriate in patellar instability addressed by MPFL reconstruction due to decreased lateral stability and inappropriate adjustment in patellofemoral contact pressures.MethodsA FE in-silico model of the patellofemoral joint was developed and validated. The model was used analyze the effect of lateral retinacular release in association with MPFL reconstruction on patellofemoral contact pressures, contact area, and lateral patellar displacement during knee flexion.ResultsMPFL reconstruction alone results in restoration of patellofemoral contact pressures throughout the entire range of motion (0–90°), mimicking the results from healthy condition. The addition of the lateral retinacular release to the MPFL reconstruction resulted in significant reductions in both patellofemoral contact pressure and contact area. Lateral retinacular release resulted in more lateral patellar displacement during the mid-flexion knee range of motion.ConclusionsCombination of lateral retinacular release with MPFL reconstruction in patients with increased TT-TG is not recommended as MPFL reconstruction alone for first-line management of recurrent patellar instability offers a greater biomechanical advantage and restoration of contact forces to resemble that of the healthy knee. The presented biomechanical data outlines the effect of concomitant MPFL reconstruction and lateral retinacular release to help guide surgical planning for patients with recurrent patellar instability due to malalignment.     

Three-dimensional assessment of patellofemoral anatomy: Reliability and reference ranges

BackgroundThree-dimensional (3D) imaging and analysis offer new possibilities in preoperative diagnostics and surgical planning. Simultaneous 3D analysis of the joint angles and the patellofemoral anatomy allow for a realistic assessment of bony pathologies in patients with patellofemoral complaints. This study aims to develop a standardized and validated assessment of the 3D patellofemoral morphology and to establish reference ranges.MethodsThirteen patellofemoral anatomic landmarks were defined on 3D bone models of the lower limbs based on computer tomography data and evaluated regarding inter- and intra-observer variability. Further, 60 3D models of the lower limbs of young subjects without any previous knee operation/injury were assessed and rescaled reference values for relevant patellofemoral indices were obtained.ResultsThe mean inter- and intra-observer deviation of all landmarks was below 2.3 mm. The interobserver intraclass correlation coefficient (ICC) was between 0.8 and 1.0 and the intra-observer ICC between 0.68 and 0.99 for all patellofemoral parameters. The calculated reference ranges are: Insall–Salvati index 1.0–1.4; patella tilt 6–18°; patella shift −4 to 3 mm; patella facet angle 118–131°; sulcus angle 141–156°; trochlear depth 3–6 mm; tibial-tuberosity to trochlear groove distance (TT-TG) 2D 14–21 mm; TT-TG 3D 11–18 mm; lateral trochlear inclination 13–23°; trochlear facet angle 43–65°.ConclusionThe demonstrated 3D analysis of the patellofemoral anatomy can be performed with high inter- and intra-observer correlation. Applying the obtained reference ranges and using existing 3D assessment tools for lower limb alignment, a preoperative 3D analysis and planning for complex knee procedures now is possible.     

Lateral patellar tilt and its longitudinal association with patellofemoral osteoarthritis-related structural damage: Analysis of the osteoarthritis initiative data

BackgroundIncrease in lateral patellar tilt-(LPT) can cause increased pressure on the lateral facet of the knee and can lead to patellar or femoral cartilage damage and further osseous changes. This study aims to test the hypothesis whether there is an association between increased LPT and MRI-based patellofemoral osteoarthritis-(OA) features at baseline and their worsening over a 2-year follow-up in participants of the Osteoarthritis Initiative-(OAI).MethodsRecorded clinical and imaging data of 600 participants in the FNIH-OA biomarkers consortium was extracted from its database. The LPT-(as the angle between the longest patella diameter and posterior aspect of condyles) was measured using the axial knee MRI. Associations of LPT (every 5° increase) with MRI OA Knee Scoring-(MOAKS) for OA-related features, including cartilage and bone marrow lesions (BMLs) in addition to knee cartilage volume at baseline and their worsening after 2-year follow-up were assessed using regression models adjusted for several possible confounders.ResultsThe mean LPT angle in this sample was 8.84° ± 5.19. In baseline, higher LPT was associated with lower cartilage volumes and higher cartilage lesions and BMLs MOAKS scores in the lateral trochlear and patellar subregions. Over the follow-ups, subjects with higher LPT measures in the baseline showed higher odds of experiencing BML score worsening in the lateral trochlear subregion-(OR:1.25[1.01–1.56]) over the 2-year follow-ups.ConclusionsIncrease in LPT measures may be associated with OA-related features in the trochlear subregion. Therefore, aside from its use as an indicator of patellofemoral instability syndrome, LPT may be associated with longitudinal progression of patellofemoral OA.     

The influence of asymmetric quadriceps loading on patellar tracking — An in vitro study

BackgroundIn patients with anterior knee pain and patellar instability, a specific training of the quadriceps muscle – especially the vastus medialis – is often recommended, although the practicability is discussed controversially and the proof of a measurable clinical effect is difficult. Therefore, this in vitro study investigates the influence of asymmetric muscle loading on the motion of the human patella.MethodsSeven human knee specimens were tested in a specially developed knee simulator. During simulated weight-bearing knee flexion, the kinematics of tibia, femur and patella were measured using an ultrasound motion capture system. The quadriceps forces were controlled to achieve a constant ankle force over the whole flexion range which is assumed to represent almost physiological loading. Three different force distributions of the quadriceps were tested — a central, equally distributed load as well as mainly lateral and medial loads.ResultsA significant influence of different quadriceps force distributions was found for patellar tilt around a proximodistal axis (up to 1.7°) and patellar rotation around an anteroposterior axis (up to 3.8°) with respect to the femur. Interestingly, the patellar mediolateral shift was influenced only marginally (< 1.5 mm).ConclusionsSpecific muscle training might help patients with patellofemoral pain and cartilage damage by a slight modification of the kinematics, but we could show that even highly asymmetric quadriceps loads only led to a small alteration of the mediolateral shift in case of a physiologic anatomy of the trochlear groove.     

Patellar resurfacing has minimal impact on in vitro tibiofemoral kinematics during deep knee flexion in total knee arthroplasty

BackgroundWhile patellar resurfacing can affect patellofemoral kinematics, the effect on tibiofemoral kinematics is unknown. We hypothesized that patellar resurfacing would affect tibiofemoral kinematics during deep knee flexion due to biomechanical alteration of the extensor mechanism.MethodsWe performed cruciate-retaining TKA in fresh-frozen human cadaveric knees (N = 5) and recorded fluoroscopic kinematics during deep knee flexion before and after the patellar resurfacing. To simulate deep knee flexion, cadaver knees were tested on a dynamic, quadriceps-driven, closed-kinetic chain simulator based on the Oxford knee rig design under loads equivalent to stair climbing. To measure knee kinematics, a 2-dimensional to 3-dimensional fluoroscopic registration technique was used. Component rotation, varus-valgus angle, and anteroposterior translation of medial and lateral contact points of the femoral component relative to the tibial component were calculated over the range of flexion.ResultsThere were no significant differences in femoral component external rotation (before patellar resurfacing: 6.6 ± 2.3°, after patellar resurfacing: 7.2 ± 1.8°, p = 0.36), and less than 1° difference in femorotibial varus-valgus angle between patellar resurfacing and non-resurfacing (p = 0.01). For both conditions, the medial and lateral femorotibial contact points moved posteriorly from 0° to 30° of flexion, but not beyond 30° of flexion. At 10° of flexion, after patellar resurfacing, the medial contact point was more anteriorly located than before patellar resurfacing.ConclusionDespite the potential for alteration of the knee extensor biomechanics, patellar resurfacing had minimal effect on tibiofemoral kinematics. Patellar resurfacing, if performed adequately, is unlikely to affect postoperative knee function.     

髌股关节形态学与髌骨软化症之间相关性研究

目的　通过MRI进行髌股关节形态学参数测量,分析髌股关节形态与髌骨软化症之间的关联性。 方法　371例接受膝关节MRI检查的成人患者,诊断为髌骨软化症（chondromalacia patellae,CP）者纳入CP组（n=124）,排除CP者纳入对照组（n=247）,按性别分组计算CP患病率。通过MRI轴位片测量两组患者的外侧髌股角、滑车沟角、滑车沟深和外侧滑车倾斜角,根据软骨损伤的程度进一步将CP组分为CP（轻型）及CP（重型）两组。运用t检验对比CP组与对照组以及CP（轻型）组与CP（重型）组的各个参数组间差异。进一步运用χ2检验分析髌骨倾斜及滑车发育不良与CP的相关性。 结果　CP的患病率为33.42%（124/371）,女性为49.35%（76/154）,男性为22.12%（48/217）,女性高于男性（P <0.01）;CP组与对照组在外侧髌股角（P =0.00）,滑车沟角（P =0.00）,滑车沟深（P =0.00）及外侧滑车倾斜角（P =0.02）上均有显著性差异。CP（轻型）组与CP（重型）组在外侧髌股角、滑车沟角、滑车沟深、外侧滑车倾斜角上均未见统计学差异（均P >0.25）。无论是否考虑性别因素,髌骨倾斜与滑车发育不良均与CP存在显著相关性（P =0.00）。 结论　髌骨倾斜及滑车发育不良与CP显著相关,但与CP的严重程度无关。     

The effect of hip adduction angle on patellar position measured using real time ultrasound scanning

IntroductionThere are limited in vivo studies investigating the influence of the Iliotibial Band (ITB) on patellar position, despite numerous references in the literature to this relationship. The purpose of this study was to investigate how the ITB influences patellar position, in vivo, indirectly through alteration of frontal plane hip position.MethodTwelve healthy, asymptomatic, male subjects (age 23 ± 2.6 years) had their patellar position examined using real time ultrasound scanning. The knee was passively placed into 20° flexion and combined with hip neutral, 20° hip adduction and 20° hip abduction. Mean patellar position (distance from the lateral border of the patella to the edge of the intersection of the trochlear groove and lateral femoral condyle) was measured, with the smaller values representing a position whereby the patella is drawn more laterally and closer to the lateral femoral condyle.ResultsMean patellar position for neutral was 8.1 mm (± 1.72 mm). Following 20° hip abduction the mean patellar position was 8.9 mm (± 1.79 mm), this was a statistically significant change in patellar position (p = 0.003). Following 20° hip adduction the mean patellar displacement was 7.3 mm (± 1.4 mm) which, again, was a statistically significant change in patellar position (p = 0.009). The results indicate that with the hip adduction the patella was positioned significantly more laterally (smaller value for distance).DiscussionThe results of this study support the hypothesis that hip adduction which is likely to create loading and lengthening of the ITB causes significantly greater lateral displacement of the patella, than when the hip is abducted and the ITB unloaded.Level of evidence: 2b individual cohort study.     

Dynamic tracking influenced by anatomy following medial patellofemoral ligament reconstruction: Computational simulation

Background

Continued patellar instability can occur following medial patellofemoral ligament (MPFL) reconstruction. Computational simulation of function was used to investigate the influence of the lateral position of the tibial tuberosity, trochlear dysplasia and patella alta on lateral patellar tracking following MPFL reconstruction.

内侧髌股韧带重建治疗复发性髌骨脱位疗效观察

目的 探讨内侧髌股韧带重建治疗复发性髌骨脱位的临床效果.方法 回顾性分析湖北省荆州市中心医院2017年1月至2019年6月通过关节镜辅助下内侧髌股韧带双束重建治疗的29例复发性髌骨脱位患者的临床资料.其中,男10例,女19例,年龄14.0～29.5岁,平均19.4岁.测量TT-TG距离、髌骨倾斜角,计算Caton指数....     

Medial patellofemoral ligament reconstruction with autologous gracilis tendon: Clinical and radiological outcomes at a mean 6 years of follow up

BackgroundThe medial patellofemoral ligament (MPFL) is considered the primary soft tissue restrain to lateral translation of the patella during the first 15–30 degrees of knee flexion. The primary restraint thereafter is the slope of the lateral wall of the trochlea. A plenty of procedures are described in literature for MPFL reconstruction with different types of graft, angle of knee flexion for fixation and rehabilitation protocols. In this study we used MPFL reconstruction with doubled autologous gracilis tendon with the Schottle’s technique. The aim of our study is to evaluate outcomes at medium-long term follow up of MPFL reconstruction.MethodsPatients who underwent arthroscopic MPFL reconstruction for recurrent patellar dislocation were followed up for a minimum of 2 to 10 years. Patient-reported outcomes including the Kujala, Visual Analogue Scale (VAS) score were collected preoperatively and postoperatively. Clinical complications such as loss of ROM, recurrent sub-luxation or dislocation were recorded.ResultsA total of 38 patients with recurrent patellar dislocation were treated with MPFL reconstruction and data were available for final follow up (mean 72.3 months, SD 33.6). Mean age at time of surgery was 23.4 (SD 7.8). Mean number of dislocations before surgery was 7.1 (SD 10.5). Recurrent dislocations were not observed in any of the patients treated at last follow-up. Significant clinical improvements were also noted with Kujala and VAS score. Patellar tilt angle decreased significantly from pre to post-operative.ConclusionOur study demonstrated that MPFL reconstruction with patellar suture anchors fixation using autologous gracilis tendon is an effective, safe and reliable method for treating recurrent patellar dislocation.     

Reconstruction of patellar tendon rupture after total knee arthroplasty using polyethylene cable

BackgroundPatellar tendon rupture is a devastating complication after total knee arthroplasty (TKA). Different strategies have been used to reconstruct or augment direct repairs.MethodsAcute patellar tendon ruptures after TKA were treated using ultra-high molecular weight polyethylene cable (Nesplon cable) for augmentation in four patients. Nesplon cables were inserted anteriorly through the quadriceps just above the patella, and drill holes were placed in the tibial tubercle with one in figure-of-eight fashion and the other in cerclage configuration. Clinical evaluations were performed using range of motion and Knee Society Score at the time of last follow-up. Mean follow-up was 3.5 years.ResultsPostoperatively, mean flexion was 119° and mean extension was 0° in all cases. No knees showed extension lag. Mean knee score was 93.8 and mean function score was 63.8. Infection occurred in one case.ConclusionPatellar tendon reconstruction with Nesplon cable was favorable with good clinical outcomes.     

The patella morphology in trochlear dysplasia--a comparative MRI study

BACKGROUND: Trochlear dysplasia is suspected to have a genetic basis and causes recurrent patellar instability due to insufficient anatomical geometry. Numerous studies about trochlear morphology and the optimal surgical treatment have been carried out, but no attention has been paid to the corresponding patellar morphology. PURPOSE: The aim of this study was the evaluation of the patellar morphology in normal and trochlear dysplastic knees. STUDY DESIGN: Biometric analysis. METHODS: Twenty two patellae with underlying trochlear dysplasia (study group--SG) were compared with 22 matched knees with normal trochlear shape (control group--CG) on transverse and sagittal MRI slices. We compared transverse diameter, cartilaginous thickness, Wiberg-index and -angle, length and radius of lateral and medial facet, patellar shape and angle, retropatellar length, and type of trochlear dysplasia. For statistical analysis we used the Wilcoxon signed ranks test. RESULTS: The transverse and sagittal diameter, mean length of medial patellar facet, and mean cartilaginous and subchondral Wiberg-index showed statistical differences between the two groups. CONCLUSIONS: Although the insufficient trochlear depth and decreased lateral trochlear slope are responsible for patellofemoral instability, the patella shows morphological changes in trochlear dysplastic knees. Its overall size and the medial facet are smaller. Although the femoral sulcus angle is larger, the Wiberg-angle and -index are equal to the control group. This may indicate that the patellar morphology may not be a result of missing medial patellofemoral pressure in trochlear dysplastic knees, but a decreased medial patellofemoral traction. This seems to be caused by hypotrophic medial patellofemoral restraints in combination with an increased lateral patellar tilt, both resulting in a decreased tension onto the medial patella facet. Whether there is a genetic component to the patellar morphology remains open.     

Arthroscopic repair of medial patellofemoral ligament avulsion in acute patellar dislocation in skeletally immature patient - A case report

Acute patellar dislocation is a severe injury to the knee and usually manifests with symptoms such as giving way, a sensation of lateral displacement of the patella accompanied by hemarthrosis and tenderness over the medial epicondylar region to palpation. Spontaneous reduction of the patella makes the diagnosis more difficult in initial evaluation. Radiographs often show a small bony avulsion at the medial border of the patella, which may represent an injury to the medial restraints. Magnetic resonance imaging may show a bone bruise on the medial patella, and/or on the lateral femoral condyle. The medial patellofemoral ligament (MPFL) may be avulsed distally, proximally or sustain in interstitial tear. Arthroscopic findings include hematoma and chondral or osteochondral lesions located on the central or medial facet of the patella or on the anterior lateral femoral condyle. We report a case of a patellar avulsion of medial patellofemoral ligament in a skeletally immature patient.     

A new 3D software for analysis and planning of lower limb and patellofemoral alignment: Reliability and accuracy

BackgroundThe new software, mediCAD® 3D Knee Sport (mediCAD Hectec GmbH, Altdorf/Landshut, Germany), promises to combine automated digital 3D bone model generation, 3D analysis of lower limb geometry including analysis of the patellofemoral joint, and osteotomy planning. The aim of this study was to evaluate its reliability and accuracy.MethodsIn this retrospective multi-observer study, three post-mortem CTs were analysed by three observers at three points in time. Reliability was evaluated by calculating the intraclass correlation coefficient (ICC) of interobserver agreement. Accuracy was evaluated using the mean deviation D from the mean and the standard deviation SD from D.ResultsTen of 18 alignment parameters showed excellent, two good and three moderate interobserver agreement. Poor agreement was found for the mechanical medial proximal tibial angle, the trochlear sulcus angle and trochlea depth. Mean interobserver ICC of all parameters ranged from 0.32 to 0.99. Fifteen of 18 parameters showed a low mean deviation D from the mean of < 2 mm / 2°. Three parameters related to the patellofemoral joint showed medium or high D (patella tilt, trochlear sulcus angle, patellar ridge angle). These parameters also showed the highest values for the SD of D. The trochlear sulcus angle was found to be the only parameter with high mean deviation (D ≥ 5 mm/5°) with D being 5.67 ± 3.23°.ConclusionsThe current version of the software achieves good interobserver reliability and accuracy with the exception of a few measurement parameters.     

Association and impact of patellofemoral dysplasia on patellofemoral arthropathy and arthroplasty

BackgroundThe association of patellar and trochlear anomalies resulting in isolated patellofemoral osteoarthritis has often been postulated but rarely studied. The purpose of this study was to examine the association of patellofemoral dysplasia, specifically trochlear anomalies, which are a cause for degenerative disease and may result in a worse outcome after arthroplasty for isolated patellofemoral arthritis.MethodsEighteen consecutive patients who underwent robotic image-based patellofemoral arthroplasty were compared with an age and sex-matched group of patients who underwent medial unicompartmental arthroplasty using the same image-based navigation system and had no patellofemoral, lateral disease or malalignment.The compared parameters were the patellofemoral–trochlear angle and Dejour score in the preoperative radiographs and patellofemoral–trochlear angle and internal rotation of the trochlea compared to the intercondylar line in the proximal, middle and distal trochlea.ResultsSignificantly higher rates of patella alta (T = 5, P = 0.0001) and trochlear dysplasia (6% vs. 55%) were found, as manifested by an increase in the trochlear angle and Dejour score. Furthermore, the trochlea was found to have a higher degree of internal rotation in patients with isolated patellofemoral arthritis compared to the control group.ConclusionsIn conclusion, patellofemoral anomalies such as patella alta and trochlear dysplasia are present in association with isolated patellofemoral arthritis. Isolated patellofemoral arthritis is also associated with higher rates of trochlear internal rotation. Correction of this internal rotation is essential in the success of arthroplasty in patients with patellofemoral disease.Level of evidenceLevel III study, It is a case control study.