Development of the femoral trochlear groove in rabbits with patellar malposition

Development of patellofemoral osteoarthritis with knee joint malalignment and lateral patellar dislocation after hindlimb suspension in growing rats

Knee malalignment is a risk factor for patellar instability and patellofemoral osteoarthritis (PFOA), but etiologies remain unknown. We investigated the potential effects of decreased weight loading during growth on knee alignments and patellofemoral (PF) joint pathology. Hindlimb suspension (HS) was performed in 4-week-old female rats for 2, 4, and 8 weeks (HS groups). Age-matched rats were used as controls. Three-dimensional reconstructed images of the knee were obtained using X-ray computed tomography. Tibial tubercle-trochlear groove (TT-TG) distance, patellar tilt angle, and bisect offset were measured as indices of knee alignment. Histological analysis was also performed to evaluate the changes in cartilage and synovium in the PF joints. At Week 8, TT-TG distance, patella tilt angle, and bisect offset were significantly larger in the HS group than in the control group, respectively, indicating tibial external rotation, outward patellar tilt, and external displacement of the patella. Lateral patellar dislocation was frequently found in the HS group at Week 8 (five of eight knee joints, p < 0.05). Degenerative changes in the cartilage of the trochlear groove were observed at Week 8, and synovial changes such as hypertrophy and synovitis were observed at Weeks 4 and 8. Correlation analyses revealed significant relationships between the Mankin score and bisect offset, and between the OARSI synovitis score and all knee alignments indices. These results suggest that decreased weight loading on the lower extremities in growing rats resulted in knee malalignments characterized by external rotation of tibia and high incidence of lateral patellar dislocation with concomitant PFOA.

Changes in the femoral trochlear induced with estradiol exposure, an experimental study on rats

BACKGROUND

It is well known that estrogen is closely related to bone and joint tissue. Findings indicate that estradiol, injected during pregnancy, passes through the placental barrier and reaches the fetuses in utero where it exerts its action. Since trochlea appears well established in the prenatal period, however, whether trochlear dysplasia is related to estradiol exposure has not been confirmed, and the pathological process of estradiol exposure-induced trochlear dysplasia remains unclear. This study aimed to establish an estradiol exposure animal model in fetuses and to analyze the morphology of the femoral trochlear in neonatal rats.

METHODS

30 pregnant Wistar rats provided by the local Animal Center were assigned randomly into three groups, a high dose estradiol injection group, a low dose estradiol injection group and a blank control group. Gross, cross-sectional observation, histological staining measurement and microcomputed tomography of the rat offspring were conducted to evaluate the morphological changes of the femoral trochlea.

RESULTS

The incidence of trochlear dysplasia increased with the concentration of estradiol injection. Gross and cross-sectional observation showed a shallower trochlea groove in two groups with estradiol injection. Histological staining measurement indicated that the trochlear sulcus angle and trochlear sulcus depth were significantly different between the two groups with estradiol injection and the blank control group at 0,5 and 10 days after birth. Subchondral bone loss was observed in the two estradiol injection groups by micro-CT, and the bone loss was found to deteriorate over time.

CONCLUSION

In this study, estradiol exposure in fetuses had an adverse effect on intrauterine development and could induce trochlear dysplasia and bone loss in rat offspring. In addition, this study also showed that the higher concentration of estradiol injection in pregnant rats, the more incidence of trochlear dysplasia in rat offspring.

Ultrasound evaluation of the femoral trochlea in newborns: incidence of trochlear dysplasia and associated risk factors

This study aimed to describe the femoral groove morphology using ultrasound in children under 6 months, estimate the incidence of trochlear dysplasia, and evaluate associated risk factors. A prospective study included 298 patients who underwent universal ultrasound screening for hip dysplasia [developmental dysplasia of the hip (DDH)] and knee ultrasound. Measurements of sulcus angle (SA), trochlear depth (TD), and trochlear facet asymmetry (TFA) were analyzed. Trochlear dysplasia was considered present if the ASO was ≥159°. Reproducibility was assessed using the intraclass correlation coefficient (ICC) in 60 knees. Logistic regression adjusted for confounders, presenting odds ratios (OR) and 95% confidence intervals (CI). Significance was set at P < 0.05. Analysis included 596 knees (298 patients). Females accounted for 51% of patients, with 7% having breech presentation, 4.4% DDH, 6.4% family history of DDH, and 5% family history of patellofemoral instability. ICC showed excellent agreement for SA and TD, but poor for TFA. Trochlear dysplasia incidence was 3% (9/298; 67% bilateral). Median (IQR) values were 147.5 (144.0-150.5) for SA, 2.4 (2.2-2.8) for TD, and 1.1 (1.0, 1.1) for TFA. Breech presentation (OR, 9.68; 95% CI 1.92-48.71, P = 0.006) and concomitant DDH (OR 6.29, 95% CI 1.04-37.78, P = 0.044) were associated with trochlear dysplasia. Ultrasound effectively evaluates femoral groove morphology and diagnoses trochlear dysplasia in newborns. Trochlear dysplasia incidence was 3%, with a 10-fold higher risk in breech presentation and 6-fold higher risk in concomitant DDH. Standardized screening and timely treatment protocols should be further investigated. Level of evidence: Diagnostic Level II.

Early Identification and Treatment of Trochlear Knee Dysplasia

A shallow sulcus characterizes trochlear dysplasia (TD) of the femoral trochlea, which can lead to chronic pain or instability of the patellofemoral joint. Breech presentation at birth has been identified as a risk factor for developing this condition, which an ultrasound can identify early. Early treatment could be considered at this stage, given the potential for remodelling in these skeletally immature patients. Newborns with breech presentation at birth who meet the inclusion criteria will be enrolled and randomised in equal proportions between treatment with the Pavlik harness and observation. The primary objective is to determine the difference in the means of the sulcus angle between the two treatment arms at two months. Ours is the first study protocol to evaluate an early non-invasive treatment for TD in the newborn with breech presentation at birth using a Pavlik harness. We hypothesised that trochlear dysplasia could be reverted when identified and treated early in life with a simple harness, as it is done with developmental dysplasia of the hip.

The Onset and Development of Patella Alta in Children With Patellar Instability

BACKGROUND

Patella alta is an anatomic risk factor for patellar instability in adolescents that is also linked to the risk factor of trochlear dysplasia. This study aims to determine the age of onset and age-related incidence of patella alta in a pediatric population of patients with patellar instability. We hypothesized that patellar height ratios would not increase with age, suggesting a congenital rather than the developmental origin of patella alta.

METHODS

A retrospective cross-sectional cohort of patients was collected with the following inclusion criteria: patients aged 5 to 18 who had a knee magnetic resonance imaging performed from 2000 to 2022 and the International Classification of Diseases code for patellar dislocation. Demographic information and details of the patellar instability episode(s) were collected with a chart review. Sagittal magnetic resonance imaging was used to measure Caton-Deschamps Index (CDI) and the Insall-Salvati Ratio (ISR) by 2 observers. Data were analyzed to assess for associations between patellar height ratios and age of the first dislocation and to assess if the proportion of patients categorized as having patella alta changed with age.

RESULTS

The 140 knees included in the cohort had an average age of 13.9 years (SD=2.40; range: 8-18) and were 55% female. Patella alta was present in 78 knees (55.7%) using CDI>=1.2 and in 59 knees (42.1%) using ISR>=1.3. The earliest age patella alta was observed was at age 8 using CDI>=1.2 and age 10 using ISR>=1.3. There were no statistically significant associations between CDI and age without adjustment (P=0.14) nor after adjustment for sex and body mass index (P=0.17). The proportion of knees above the CDI threshold for patella alta to the knees below the cutoff did not show a significant change with age (P=0.09).

CONCLUSIONS

Patella alta, as defined by CDI, is seen in patients as young as 8 years old. Patellar height ratios do not change with age in patients with patellar dislocation, suggesting that patella alta is established at a young age rather than developing during the adolescent years.

LEVEL OF EVIDENCE

Level III-diagnostic, cross-sectional.

Effects of hindlimb suspension on development of proximal and distal femur morphological abnormalities in growing rats

Although morphological abnormalities of the femur are known predisposing factors for numerous musculoskeletal disorders, the etiology of these abnormalities is poorly understood. This study aimed to investigate whether femoral morphogenesis is affected by hindlimb suspension (HS) in growing rats. We used 41 four-week-old female rats in this study. In the HS groups, rats were suspended from their tails for 2, 4, and 8 weeks. Age-matched animals were used as controls. We examined morphological indices of the femur using three-dimensional reconstructed images from X-ray computed tomography. The femoral neck anteversion angle (AVA) was higher with growth in the experimental groups and did not differ in control groups. The AVAs in the HS groups were larger than controls at any time point. In the control groups, the trochlear angle (TA) was higher, rotating inward with growth, but did not differ in the HS groups. The TAs in the HS groups were smaller and rotated more outward compared with the control groups at any time point. The height ratios of the medial and lateral condyles (MC/LC), an asymmetry index, were larger in the HS groups compared to controls at any time point. There were strong relationships between proximal (AVA) and distal morphologies, such as the TA (Spearman's coefficient [r_s ] = -0.80, p < 0.001) and MC/LC (r_s  = 0.79, p < 0.001). Our data suggest that sufficient physical activity in early life may protect against morphological femur abnormalities associated with hip and knee joint diseases.

Patellar development after patella instability and early reduction in growing rabbits

BACKGROUND

Patella-shaped disorder has been considered as a predisposing factor for patella instability. But the influence of early patella reduction for patellar development remains unclear. This study aimed to evaluate whether early operation in patella instability could improve patella morphology in growing rabbits.

METHODS

Fifty rabbits (1-month-old) were included in the study. The control group underwent no surgical procedures. The two experimental groups (reduction group and non-reduced group), underwent medial soft tissue restraint release surgery. The reduction group, rabbits underwent the medial soft tissue sutura surgery in order to stabilize the patella 2 months after release surgery. The non-reduced group, rabbits did not undergo suture surgery. Computed Tomography (CT) scans analysis in two experimental endpoints (2, 5 months after release surgery) were selected to evaluate the transverse diameter, thickness, Wiberg index and Wiberg angle. Gross observation was conducted to assess morphological changes of the patella.

RESULTS

CT scans showed significant difference in the mean transverse diameter, Wiberg angle between the two experimental groups and the control group 2 months after release surgery. 5 months after release surgery, the indices of patella were found no statistically difference in the reduction group versus the control group. However, the transverse diameter, Wiberg angle in the non-reduced group were significantly differences than that in the reduction group (P < 0.05). Gross observation showed a flattened articular surface of the patella in the non-reduced group.

CONCLUSIONS

The results indicated that patella instability may lead to patella-shaped disorder, showing a flattened morphology. Early patella reduction can improve the patella morphology in growing rabbits.

Abnormal patellar loading may lead to femoral trochlear dysplasia: an experimental study of patellar hypermobility and patellar dislocation in growing rats

BACKGROUND

This animal study aimed to explore the effects of patellar hypermobility and patellar dislocation on the developing femoral trochlea.

METHODS

Seventy-two 3-week-old Wistar rats were randomly divided into three groups. The sham group (SG) underwent simple incision and suture of the skin and subcutaneous tissue; the patellar hypermobility group (PHG) underwent medial and lateral retinacular release and pie-crusting technique for the patellar ligament; the patellar dislocation group (PDG) underwent plication of the medial patellofemoral retinaculum. Twelve rats in each group were euthanized at 3 and 6 weeks postoperatively, respectively, and specimens were collected. The bony sulcus angle (BSA), cartilaginous sulcus angle (CSA), trochlear sulcus depth (TSD), and thickness of the cartilage on the lateral facet (CTL), medial facet (CTM), and center (CTC) of the trochlea were measured on hematoxylin and eosin-stained sections.

RESULTS

In the PHG and PDG, the femoral condyles became blunt, the trochlear groove became shallower, and cartilage became thicker compared with the SG. Compared with the SG, the PHG and PDG had significantly larger BSA and CSA values at 3 (p < 0.05) and 6 weeks (p < 0.005), and a significantly shallower TSD (p < 0.05). At 3 weeks, all cartilage thicknesses in the PHG and the CTC and CTM in the PDG were significantly thinner than in the SG (PHG vs. SG: p = 0.009 for CTL, p < 0.001 for CTM, p = 0.003 for CTC; PDG vs. SG: p = 0.028 for CTC, p = 0.048 for CTM). At 6 weeks, the CTC was thicker in the PHG and PDG than the SG (PHG vs. SG: p = 0.044; PDG vs. SG: p = 0.027), and the CTL was thinner in the PDG than the SG (p = 0.044).

CONCLUSION

Patellar hypermobility and patellar dislocation may result in trochlear dysplasia that worsens with age. Excessive or insufficient loading leads to trochlear dysplasia.

The pathologic double contour sign and the trochlea shape patterns can diagnose trochlea dysplasia

OBJECTIVES

The goal of this study is to describe the distinct morphologic patterns of the normal and dysplastic trochleae, the trochlear shape patterns (TSP) seen on the axial views of MRI scans.

METHOD

Two cohorts of patients were used for comparison. Cohort 1: MRI scans of 100 patients with no history of patella instability. Cohort 2: MRI scans of 66 patients diagnosed with severe trochlea dysplasia and patella instability. The presence of the pathologic double contour (PDC) sign and the type of TSP were identified in the axial views at the level of three specific anatomical references: Trochlear Specific Zone 0 (TSZ 0), posterior femoral condyle line (PFCL) and transverse distal femoral physis line (tv-DFPL). The pathologic double contour sign is an area of flat or convex lateral trochlea which is elevated over the contour of the medial femoral condyle. Three basic morphologic patterns of trochlear shape were identified. TSP type 1 (normal trochlea): There is no PDC. There is a clearly defined sulcus delineating the lateral and medial trochlear facets (sulcus angle <165°). TSP type 2 (normal but shallow trochlea): There is no PDC. The trochlear groove is shallow (sulcus angle >165°), but the lateral and medial facets are present. TSP type 3: This pattern is characterised by the presence of a PDC. The chi-square test was used to determine whether the distribution of the TSP was the same between the two cohorts at the anatomical reference lines.

RESULTS

The differences observed in distribution of the TSP between the two cohorts were statistically significant. There was a strong positive correlation between the morphology of the trochlea (TSP) and patella instability. All patients in the patella instability cohort showed a PDC.

CONCLUSION

Normal trochleae show TSP type 1 and 2 proximal to the tv-DFPL. The presence of the pathologic double contour sign and trochlea shape pattern type 3 (TSP 3) proximal to the tv-DFPL (PFCL or TSZ 0) are diagnostic of trochlea dysplasia.

Can Traditional Straight-leg Swaddling Influence Developmental Dysplasia of the Femoral Trochlea? An In Vivo Study in Rats

BACKGROUND

It has been reported that trochlear dysplasia occurs very early in development, and environmental factors like swaddling may cause developmental dysplasia of the hip, which is associated with a shallower trochlear groove. However, to our knowledge, there are no definitive studies about the relationship between trochlear dysplasia and traditional straight-leg swaddling.

QUESTIONS/PURPOSES

Using a rat model of femoral trochlear dysplasia, we asked: Does straight-leg swaddling for 1 and 2 weeks in newborn Wistar rats alter the femoral trochlea with respect to (1) gross morphology, (2) histologic appearance, as well as (3) trochlear sulcus angle, width, and depth?

METHODS

Eighty-four newborn Wistar rats (44 females and 40 males) were divided into two equal groups: 42 in the unswaddled group and 42 in the swaddled group; each group was comprised of 22 females and 20 males. In the swaddled group, the rats were wrapped in surgical tape to maintain hip and knee extension to simulate traditional human straight-leg swaddling. To determine whether longer periods of swaddling were associated with more severe trochlear dysplasia, 21 rats in each group were euthanized at 1 and 2 weeks, respectively, and the gross morphology of the femoral trochlea was observed by one observer blinded to condition. Then hematoxylin and eosin staining of the femoral trochlea was performed and the distribution and number of the chondrocytes of the trochlear groove were viewed through a microscope. The trochlear sulcus angles, depth, and width were measured by an experienced technician blinded to condition.

RESULTS

By observing the gross morphology, we found that the trochlear groove in the swaddled group became qualitatively flatter compared with the unswaddled group at 1 week, and at 2 weeks, the trochlear groove became much shallower. At 1 and 2 weeks, histologic examinations showed obvious qualitative changes in the distribution and number of chondrocytes of the trochlear groove in the swaddled than in the unswaddled groups. In the swaddled group, trochlear dysplasia was more common at 2 weeks, occurring in 62% (26 of 42 [16 of 22 females and 10 of 22 males]) versus 33% (14 of 42 [8 of 22 females and 6 of 20 males]) at 1 week. At 1 week, the swaddled group showed more trochlear dysplasia compared with the unswaddled group as measured by angle of the trochlear groove (137° ± 6° versus 132°± 3.6°, mean difference 5° [95% confidence interval 2.9° to 7.2°]; p < 0.001), depth of the trochlear grove (0.28 ± 0.04 mm versus 0.31 ± 0.02 mm, mean difference 0.03 mm [95% CI 0.01 to 0.04]; p < 0.001). At 2 weeks, the swaddled group showed more severe trochlear dysplasia than at 1 week compared with the unswaddled group as measured by the angle of the trochlear groove (135° ± 6.0° versus 128° ± 4.8°, mean difference 7° [95% CI 5.7° to 10.4°]; p < 0.001), depth of the trochlear grove (0.32 ± 0.04 mm versus 0.36 ± 0.02 mm, mean difference 0.04 mm [95% CI 0.03 to 0.06]; p < 0.001). There was no difference in the width of the trochlear sulcus between the swaddled and the unswaddled groups at 1 week (1.29 ± 0.14 mm versus 1.30 ± 0.12 mm, mean difference 0.01 mm [95% CI -0.05 to 0.07]; p = 0.73) and 2 weeks (1.55 ± 0.12 mm versus 1.56 ± 0.12 mm, mean difference 0.01 mm [95% CI -0.05 to 0.07]; p = 0.70).

CONCLUSION

Our results indicate that traditional straight-leg swaddling could induce trochlear dysplasia in this model of newborn rats. With an increased swaddling time of 2 weeks, more severe trochlear dysplasia appeared in the swaddled group.

CLINICAL RELEVANCE

Our findings suggest that traditional straight-leg swaddling may impair trochlear development in the human neonate and lead to trochlear dysplasia in infants. We believe our animal model will be useful in future work to observe and study the change of cartilage and subchondral bone in each stage of the development of trochlear dysplasia and the change of mechanotransduction-associated proteins (such as, TRPV4/ Piezo1 and CollagenⅡ) in cartilage and subchondral osteocytes. It will also be helpful to further investigate the mechanism of developmental femoral trochlea dysplasia caused by biomechanical changes.

Patellar Height Correlates Modestly With Trochlear Dysplasia: A Magnetic Resonance Imaging Analysis

Purpose

To evaluate whether there is a correlation between the position of the patella and trochlear morphology in patients with and without patellar instability using exclusively MRI measurements.

Methods

MRI scans of knees in patients with patellofemoral instability and knees of patients with an ACL (anterior cruciate ligament) tear as a control group were reviewed. Measurements of patellar position (Canton-Deschamps ratio, Patellar Trochlear Index, and lateral patellar inclination) and trochlear morphology (lateral trochlear inclination and sulcus angle) were obtained from each scan. Bivariate and multivariate analysis was performed to identify correlations between study group, demographics, and patellofemoral joint measurements.

Results

There were 70 knees in the patellofemoral instability group and 60 knees in the control group. Bivariate analysis showed a significant difference in all measurements between the patellar instability group and the control group. Multivariate analysis showed modest correlations between patellar position and trochlear morphology. The Caton-Deschamps (CD) ratio correlated with patellar trochlear index (P < .001) and lateral trochlear inclination (P < .001). The respective R-square goodness of fit was 41.1%. Patellar trochlear index correlated with CD ratio (P < .001), lateral trochlear inclination (P < .001), lateral patellar inclination (P < .001), and patellar instability group (P = .011). The R-sq goodness of fit was 37.3%. Lateral patellar inclination correlated with patellar trochlear index (P < .001), Lateral trochlear inclination (P < .001), and age at first dislocation or injury (P = .02). The R-sq goodness of fit was 68.56%.

Conclusions

Using MRI-based measurements of the patellofemoral joint, we identified modest, but significant, correlations between measures of patellar height (patellar trochlear index, CD ratio, and lateral patellar inclination) and trochlear dysplasia. This correlation is unclear and is likely multifactorial, but on the basis of this work, a causal relationship between trochlear dysplasia and patella alta cannot be established.

Clinical Relevance

Radiographic evaluation of the patella and how it relates to the surrounding boney anatomy provides important information regarding our understanding of patella instability and its treatment.

RNA-seq based integrative analysis of potential crucial genes and pathways associated with patellar instability

Patellar instability (PI) is a common knee injury in adolescents, but the crucial biomarkers and molecular mechanisms associated with it remain unclear. We established a PI mouse model and investigated PI-related changes in gene expression by RNA sequencing (RNA-seq). Differentially expressed gene (DEG) analysis and enrichment analysis were performed to identify crucial genes and pathways associated with PI. Subsequently, a protein-protein interaction, DEG-miRNA, DEG-transcription factors, and DEG-drug interaction networks were constructed to reveal hub genes, molecular mechanism, and potential drugs for PI. Finally, the reliability of the sequencing results was confirmed by real-time quantitative polymerase chain reaction (RT-qPCR) and immunohistochemistry. Upon comparison with the control group, 69 genes were differently expressed in PI, including 17 upregulated and 52 downregulated ones. The DEGs were significantly enriched in Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathway and immune responses. The protein–protein interaction network identified ten PI-related hub genes, all of which are involved in the JAK/STAT signaling pathway or inflammation-related pathways. DEG-miRNA and DEG-transcription factor networks offered new insights for regulating DEGs post-transcriptionally. We also determined potential therapeutic drugs or molecular compounds that could restore dysregulated expression of DEGs via the DGIdb database. RT-qPCR results were consistent with the RNA-seq, confirming the reliability of the sequencing data. Immunohistochemistry results suggested that JAK1 and STAT3 expression was increased in PI. Our study explored the potential molecular mechanisms in PI, provided promising biomarkers and suggested a molecular basis for therapeutic targets for this condition.

The Tibial Tubercle-Trochlear Groove Distance/Trochlear Dysplasia Index Quotient Is the Most Accurate Indicator for Determining Patellofemoral Instability Risk

PURPOSE

The primary aim of our study was to evaluate diagnostic accuracy of the tibial tubercle-trochlear groove (TT-TG) distance relative to associated quotients produced from trochlear width (TT-TG distance/TW) and trochlear dysplasia index (TT-TG distance/TDI) for detecting patellofemoral instability. Secondary aims included identifying thresholds for risk and comparing differences between cases and controls.

METHODS

Consecutive sampling of electronic medical records produced 48 (21 males, 27 females) patellofemoral instability cases (19 ± 7 years old) and 79 (61 males, 18 females) controls (23 ± 4 years old) who had a history of isolated meniscal lesion, as evaluated by magnetic resonance imaging. Standardized methods were employed with measurements executed in a blinded and randomized manner. A receiver operating characteristic curve assessed accuracy by area under the curve (AUC). The index of union (IU) was employed to identify a threshold for risk. Two-sample t-tests examined group differences. P < .05 denoted statistical significance.

RESULTS

The AUC values were .69 (.60, .79) for TT-TG distance, .81 (.73, .88) for TT-TG distance/TW, and .85 (.78, .91) for TT-TG distance/TDI. Thresholds were 14.7 mm for TT-TG distance, .36 for TT-TG distance/TW, and 1.88 for TT-TG distance/TDI. Cases demonstrated statistically significant (P < .001) greater values for each measure compared with controls: TT-TG distance (15.8 ± 4.2 mm vs 12.9 ± 3.6 mm, [1.4, 4.3]); TT-TG distance/TW (.51 ± .24 vs .31 ± .09, [.13, .27]); TT-TG distance/TDI (3.07 ± 1.55 vs 1.7 ± .7, [.9, 1.84]).

CONCLUSION

The TT-TG distance, TT-TG distance/TW, and TT-TG distance/TDI measures were 69%, 81%, and 85%, respectively, accurate for determining patellofemoral instability risk. Thresholds for risk were 14.7 mm for TT-TG distance, .36 for TT-TG distance/TW, and 1.88 for TT-TG distance/TDI. The thresholds reported in this study may help in advancing clinical decision-making.

LEVEL OF EVIDENCE

Level III, diagnostic retrospective comparative observatory trial.

What is the relationship between the breech presentation and femoral trochlear dysplasia? An experimental study of the breech presentation model in neonatal rats

Background

The relationship between breech presentation and trochlear dysplasia has been confirmed. However, the pathological process of breech-related trochlear dysplasia remains unclear. This study aimed to establish an animal model to simulate breech presentation and to analyze the pathological process of the femoral trochlea.

Materials and Methods

One hundred and twenty neonatal rats were randomly assigned into a control group and two experimental groups that were swaddled (using surgical tape) to keep the hip flexed and knees extended to simulate human breech presentation for the 5 days (short Swaddling) and the 10 days (prolonged Swaddling) of life. Gross and cross-sectional observation, histological staining measurement in two experimental time points (5 and 10 days after birth) were conducted to evaluate the morphological changes of the femoral trochlea.

Results

The incidence of trochlear dysplasia increased with the Swaddling time. Rats in the prolonged Swaddling group had the high prevalence of trochlea dysplasia (52 of 60), followed by short Swaddling group (42 of 60). Gross and cross-sectional observation showed a shallower trochlea groove in two experimental groups. Histologicalstaining measurement indicated that the trochlear sulcus angle and trochlear sulcus depth were significantly different between the experimental group and the control group since day 5 and day 10.

Conclusion

In this model, breech presentation had an adverse effect on neonatal knees and could induce trochlear dysplasia. In addition, this study also showed that the more time in breech presentation, the more incidence of trochlear dysplasia.

Clinical outcomes and predictive factors for failure with MPFL reconstruction combined with tibial tubercle osteotomy and lateral retinacular release for recurrent patellar instability

BACKGROUND

Medial patellofemoral ligament (MPFL) reconstruction combined with tibial tubercle osteotomy (TTO) and lateral retinacular release (LRR) is one of the main treatment methods for patellar instability. So far, few studies have evaluated the clinical effectiveness and assessed potential risk factors for recurrent patellar instability.

PURPOSE

To report the clinical outcomes of MPFL reconstruction combined with TTO and LRR at least three years after operation and to identify potential risk factors for recurrent patellar instability.

METHODS

A retrospective analysis of medical records for patients treated with MPFL, TTO and LRR from 2013 to 2017 was performed. Preoperative assessment for imaging examination included trochlear dysplasia according to Dejour classification, patella alta with the Caton-Deschamps index (CDI), tibial tubercle-trochlear groove distance. Postoperative assessment for knee function included Kujala, IKDC and Tegner scores. Failure rate which was defined by a postoperative dislocation was also reported.

RESULTS

A total of 108 knees in 98 patients were included in the study. The mean age at operation was 19.2 ± 6.1 years (range, 13-40 years), and the mean follow-up was 61.3 ± 15.4 months (range, 36-92 months). All patients included had trochlear dysplasia (A, 24%; B, 17%; C, 35%; D, 24%), and 67% had patellar alta. The mean postoperative scores of Tegner, Kujala and IKDC were 5.3 ± 1.3 (2-8), 90.5 ± 15.5 (24-100) and 72.7 ± 12.1 (26-86). Postoperative dislocation happened in 6 patients (5.6%). Female gender was a risk factor for lower IKDC (70.7 vs 78.1, P = 0.006), Tegner (5.1 vs 6.0, P = 0.006) and Kujala (88.2 vs 96.6, P = 0.008). Age (p = 0.011) and trochlear dysplasia (p = 0.016) were considered to be two failure factors for MPFL combined with TTO and LRR.

CONCLUSION

As a surgical method, MPFL combined with TTO and LRR would be a reliable choice with a low failure rate (5.6%). Female gender was a risk factor for worse postoperative outcomes. Preoperative failure risk factors in this study were age and trochlear dysplasia.

LEVEL OF EVIDENCE

Level IV; Case series.

Current Concepts Regarding Patellofemoral Trochlear Dysplasia

Optimal treatment of patients with patellofemoral trochlear dysplasia and recurrent patellar instability requires in-depth understanding of this complex structural anomaly. An extensive review of the literature suggests that dysplasia occurs as a result of aberrant forces applied to the patellofemoral joint in the majority of cases. Evidence supports surgical stabilization that reconstructs the medial patellofemoral and/or medial quadriceps tendon-femoral ligament without added trochleoplasty in the majority of patients with trochlear dysplasia and recurrent patellar instability. Adding tibial tubercle transfer distally, medially, or anteromedially in those who need it to treat specific deficits in alignment or articular cartilage can be beneficial in selected patients with trochlear dysplasia and recurrent patellar instability. Trochleoplasty may be appropriate in those few cases in which permanent stable patellofemoral tracking cannot be restored otherwise, but the indications are not yet clear, particularly as trochleoplasty adds risk to the articular cartilage. Improved understanding of imaging techniques and 3-dimensional reproductions of dysplastic patellofemoral joints are useful in surgical planning for patients with recurrent patellar instability and trochlear dysplasia.

Moment arm function dictates patella sagittal height anatomy: Rabbit epiphysiodesis model alters limb length ratios and subsequent patellofemoral anatomical development

Patellofemoral anatomical dysplasia is associated with patellofemoral instability and pain. The closure of the knee physis occurs at the same age as the peak incidence of patellofemoral dislocation. This study determined the effect on the patellofemoral anatomical development in a rabbit epiphysiodesis model. Twenty-four skeletally immature New Zealand White rabbits were divided into three groups (a) distal femur epiphysiodesis (FE) (b) proximal tibia epiphysiodesis (TE) (c) control; no epiphysiodesis (C) performed at 6 weeks of age. The primary endpoint was shape analysis using three-dimensional reconstructions of micro-computed tomographys (CTs) performed at 30 weeks of age. The limb length ratios (femur:tibia) were significantly different for both FE (mean 0.72, SD 0.0381, P < .001) and TE (mean 0.91, SD 0.0383, P < .001) treatment groups compared to control (mean 0.81, SD 0.0073). Patella height, as measured from the most distal point of the patella to the tibial joint surface (modified Caton-Deschamps measurement), was lower (baja) in the FE and higher (alta) for the TE, compared with the control group. Our findings suggest femoral and tibial shortening can influence the development of the patellofemoral joint, which may be dictated by moment arm function and is potentially responsible for the etiology of patella alta. Future studies are warranted to explore this association further with the view for the development of treatment options for patella alta in human patients.

Hindlimb torsional alignment changes in growing rabbits after patellar dislocation

BACKGROUND

Torsional malalignment has been considered as a risk factor for patellar dislocation. But the influence of patellar dislocation for torsional alignment development remains unknown. The present study aims to investigate whether the torsional alteration of the hindlimb occurs after patellar dislocation in growing rabbits.

METHODS

In the present study, 30 one-month-old rabbits were included. The experimental group consisted of 30 left knees of rabbits which underwent patellar lateral dislocation. The control group consisted of 30 right knees of the rabbits which no surgical procedure was performed. The Computed Tomography (CT) scan was performed after the surgery and at the point the rabbits were skeletal mature (5 months post-surgery). The angles of femoral version and tibial torsion were measured using a three-dimensional method and analyzed between the experimental group and the control group.

RESULTS

After the surgery, the femoral version and tibial torsion in the experimental and control group were not significantly different. However, 5 months after surgery, the angle of femoral version in the experimental group (-5.50 ± 6.13°) was significantly different from that in the control group (-10.90 ± 4.74°) (P < 0.05). But the angle of tibial torsion in the experimental group (7.17 ± 7.25°) and control group (4.47 ± 6.34°) were not significantly different (P = 0.144).

CONCLUSIONS

From this study, patellar dislocation can lead to alteration of femoral version in growing rabbits. So patellar dislocation may affect on lower extremity alignment. These findings may develop pathology and etiology of patellar dislocation.

Assessment of Patellar Morphology in Trochlear Dysplasia on Computed Tomography Scans

Objective

To evaluate the patellar morphology of trochlear dysplasia and normal knees in different genders and in different severities of trochlear dysplasia on CT scans.

Methods

A total of 75 patients with trochlear dysplasia (110 knees) treated at the Third Hospital of Hebei Medical University from December 2013 to December 2018 were included in an experimental group, and an age‐matched and sex‐matched cohort of 46 patients with normal trochlear shape (61 knees) were randomly selected into a control group. The experimental group was divided into a female experimental group (Group FE, 47 patients, 72 knees) and a male experimental group (Group ME, 28 patients, 38 knees); the control group was divided into a female control group (Group FC, 31 knees, 24 female patients) and a male control group (Group MC, 30 knees, 22 male patients). Furthermore, according to the severity of trochlear dysplasia, Group FE was divided into a female low‐grade dysplasia group (Group FL, 20 knees) and a female high‐grade dysplasia group (Group FH, 52 knees); Group ME was divided into a male low‐grade dysplasia group (Group ML, 16 knees) and a male high‐grade dysplasia group (Group MH, 22 knees). All participants had undergone CT scans in the supine position; the patellar width and thickness, the lateral patellar facet angle, the Wiberg angle, and the Wiberg index were measured and compared.

Results

In trochlear dysplasia knees, the mean patellar width and thickness and the lateral patellar facet angle were significantly smaller; the mean Wiberg index was significantly larger than in normal knees, regardless of gender (P < 0.05); and there was no statistically significant difference in the mean Wiberg angle (P > 0.05). In the female groups, the mean patellar width and thickness and the Wiberg angle were significantly smaller; the mean lateral patellar facet angle was significantly larger than those in the male groups (P < 0.05); and there was no significant difference in the mean Wiberg index (P > 0.05). In the low‐grade dysplasia group, the mean Wiberg index was smaller than that in the high‐grade dysplasia group (P < 0.05), regardless of gender; however, there was no significant difference in the mean patellar width and thickness, the lateral patellar facet angle, and the Wiberg angle in low‐grade and high‐grade dysplasia (P > 0.05).

Conclusion

On CT scans, the patella in trochlear dysplasia had a smaller width, a thinner thickness, a lengthened lateral facet, and a more flattened articular facet. In addition, the patellar articular facet was more prominent in female patients. With the severity of trochlear dysplasia increased, the lateral patellar facet became longer. In addition, the abnormal stress distribution on the patella influenced the patellar morphology in trochlear dysaplasia.

Four-in-one Extensor Realignment for the Treatment of Obligatory or Fixed, Lateral Patellar Instability in Skeletally Immature Knee

BACKGROUND

Congenital (fixed) and obligatory (habitual) patellar dislocations in children are a complex clinical and surgical challenge. Numerous individual surgical techniques have been described. This study aims to assess results, patient satisfaction, and complications after a combined Roux-Goldthwait procedure, vastus medialis obliquus advancement, Galeazzi procedure, and extensive, lateral release (4-in-1 extensor realignment) in the skeletally immature knee with obligatory, or fixed lateral patellar instability.

METHODS

Records of children with congenital fixed or obligatory patellar instability, who underwent the 4-in-1 procedure at a single institution, were reviewed. Clinical results included ability and time for the return to activities of daily living (ADL) and sport, recurrent instability and/or dislocation, and necessity of long-term bracing. Continued pain was assessed by the Kujala Score. Complications including infection, recurrent instability, and the necessity for secondary procedures were recorded.

RESULTS

A total of 34 patients (46 knees) mean age 10.3±2.4 years, underwent the 4-in-1 procedure with a mean postoperative follow-up of 51.6±31.5 (range, 12 to 146) months. Sixteen patients (22 knees) responded to a phone interview and questionnaire. All 16 patients returned to ADL in a mean time of 10.3±2.4 weeks. Ninety-one percent returned to sport in a mean time of 23.1±15.5 weeks. Long-term bracing was required for 6 knees after the surgery. The mean Kujala Score was 93.0±5.2 (range, 83 to 100). Complications included 6 of 34 patients (18%) with recurrent instability at the latest follow-up and 2 with superficial wound infection.

CONCLUSIONS

Patients with obligatory or fixed lateral, patellar instability who undergo the 4-in-1 procedure have good short-term results with low complication rates. Return to ADL and sporting activity with minimal pain can be expected, usually without the need for long-term bracing. The 4-in-1 procedure is a viable option for skeletally immature patients with obligatory or fixed, lateral patellar instability.

LEVEL OF EVIDENCE

Level IV-Therapeutic study.

Computed tomographic localization of the deepest portion of the femoral trochlear groove in healthy dogs

OBJECTIVE

To validate a computed tomographic (CT) method to measure the femoral trochlear groove depth (FTGD).

STUDY DESIGN

Cadaveric study.

SAMPLE POPULATION

Fifteen dogs, 26 femoral trochleae.

METHODS

Five points were identified from proximal to distal (proximal point [PP], P25, P50, P75, and distal point [DP]) along the trochlea via three-dimensional volume-rendering function on the sagittal plane and measured on multiplanar reconstruction images. Each rater repeated measurements in duplicate, unaware of the identity of the joint. The FTGD was quantitated on the anatomical specimens and statistically compared with CT measurements. Intrarater and interrater agreements were analyzed by using intraclass coefficients. Accuracy was evaluated by using either adjusted R² coefficients (R²  > 80% was considered acceptable) or Student's t test. The ratio of the patellar and the trochlear width and the ratio of the patellar craniocaudal thickness inside the trochlear groove were calculated at three different patellar locations.

RESULTS

Good to excellent intrarater and interrater agreements were observed in four of five trochlear points (P25, P50, P75, and DP), and accuracy was acceptable for these points (R²  > 80%). Computed tomographic measurements differed from the mean anatomical measurements at three of five points (PP, P50, and P75; P < .01), overestimating the FTGD by an overall mean of 0.18 mm (range, 0.02-0.3). P25 and P50 were the deepest points measured.

CONCLUSION

Computed tomography allowed precise measurements of trochlear groove depth except for the most proximal point. The deepest trochlear points were P25 and P50. P25 was the most precise and accurate point measured, while PP was the least consistent.

CLINICAL SIGNIFICANCE

The deepest portion of the trochlea groove may be located between P25 and P50. Evaluation of this CT method in dogs with patellar luxation is recommended.

Changes in Cartilage and Subchondral Bone of Femoral Trochlear Groove After Patellectomy in Growing Rabbits

OBJECTIVE

To explore the effects of patellectomy on the bony and cartilaginous morphology of the trochlear groove in growing rabbits.

METHODS

Forty-eight 4-week-old New Zealand white rabbits were randomly assigned to two groups. The control group underwent a sham surgical procedure, whereas the patellectomy group underwent patella excision surgery. Half of the rabbits in each group were sacrificed 3 months postoperatively; the rest were sacrificed 6 months postoperatively. Hematoxylin and eosin staining was performed on collected samples. Measurements included the bony and cartilaginous sulcus angles of the trochlear groove. In addition, the thickness of the articular cartilage at the deepest sulcus position (central thickness) and at the mid-position of the medial and lateral facets was measured and compared between groups.

RESULTS

Three months after surgery, histological images revealed significant differences between the control group and the patellectomy group in cartilaginous sulcus angle (144.2° ± 1.5° vs 151.9° ± 2.4°, respectively; P < 0.001). No obvious difference in bony sulcus angle was found between the groups. Six months after surgery, significant between-group differences were observed in cartilaginous sulcus angle (136.3° ± 2.5° in control group vs 160.7° ± 3.0° in patellectomy group, P < 0.001) and bony sulcus angle (136.2° ± 2.2° in control group vs 160.4° ± 2.6° in patellectomy group, P < 0.001). However, there were no significant intra-group differences between cartilaginous and bony sulcus angles in either group. Three months after surgery, significant between-group differences were detected in articular cartilage thickness at the three different positions (medial facet: 324.3 ± 14.0 μm in control group vs 391.7 ± 98.8 μm in patellectomy group, P = 0.029; central position: 362.1 ± 13.6 μm in control group vs 730.3 ± 76.8 μm in patellectomy group, P < 0.001; lateral facet: 324.6 ± 12.7 μm in control group vs 358.5 ± 38.7 μm in patellectomy group, P = 0.009). No between-group differences in cartilage thickness were found at 6 months.

CONCLUSIONS

Abnormal mechanical stress (patellectomy) during a rabbit's development can cause flattening of the femoral trochlear cartilage, followed by changes in the subchondral osseous layer. Abnormal mechanical stress is a crucial factor in the development of trochlear groove dysplasia.

The effect of increased femoral anteversion on the morphological and trabecular microarchitectural changes in the trochlea in an immature rabbit

Increased femoral anteversion (FA) has been recently demonstrated as one risk factor for recurrent patellar dislocation (RPD). However, it has been still unclear whether the increase of FA can result in patellar dislocation, and subsequent morphological and trabecular microarchitectural changes in the trochlea has not been investigated. Forty knees from 20 rabbits at 3 months of age were included. The right knees underwent surgery with internal rotation of distal femur to increase FA, with the left knees acting as internal controls. The surgical knees were called operated group, and non-operated knees were control group. Micro-CT scans for distal femur were acquired after 4 months of surgery. In the operated group, a boss located proximal to the entrance of the groove was formed. The central trochlear height was significantly greater, sulcus angle was significantly greater, both lateral and medial trochlear slope were significantly lower, and boss height was significantly greater in comparison to the control group. Regarding the microarchitectural changes, the trabecular thickness were increased by 67.5% at the groove, 33.0% and 29.5%, at the medial and lateral femoral condyle, and trabecular number were decreased by 37.8% and 26.5% at the groove and medial femoral condyle. This study provided a novel animal model of trochlea dysplasia by femoral rotational osteotomy and increased FA. These changes were associated with the load redistribution in the patellofemoral joint after the increase of FA.

The dysplastic trochlear sulcus due to the insufficient patellar stress in growing rats

BACKGROUND

Developmental factors were assumed to be the key factors that influenced the morphology of femoral trochlea. This study investigated the effects of insufficient patellar stress after birth on the morphological development of the femoral trochlea. Effects of insufficient patellar stress on femoral trochlea were investigated using surgical induced patellectomy and patellar dislocation in growing rat model.

METHODS

In this study, two experimental groups and one sham group (SG) were established. Thirty-six Wistar rats (female, 28 days of age) were randomly assigned to three groups. The patellectomy group (PG), rats underwent the patellectomy in this group. The dislocation group (DG), rats underwent the surgery-induced patellar dislocation. Histological staining (Safranin-O and fast green), Micro-computed tomographic (Micro-CT) analysis in two experimental endpoints (3, 12 weeks postoperatively) were selected to evaluate morphological changes of the femoral trochlea.

RESULTS

Articular cartilage on the trochlear sulcus was remodeled at 3 weeks after the surgery, and degenerated at 12 weeks through the histological staining. The femoral trochlear angle (FTA) did not show a significant difference at 3 week between the experimental groups and the sham group (PG vs SG P = 0.38, DG vs SG p = 0.05), but the FTA was significantly increased in experimental groups at 12 weeks(PG vs SG P = 0.001, DG vs SG p = 0.005). The Bone volume density (BV/TV), Trabecular number (Tb.N) under the trochlea groove were significantly reduced at 3 weeks postoperatively in the experimental groups (PG vs SG p = 0.001, DG vs SG p = 0.002). No significant difference was found in BV/TV and Tb. N among the three groups at 12 weeks postoperatively.

CONCLUSION

Surgical induced patellectomy and patellar dislocation leads to the dysplastic trochlear sulcus in growing rats. Besides the bone morphology of trochlear sulcus, the articular cartilage and subchondral trabecula under the trochlear sulcus were remodeled early stage after the surgery.

Surgical Treatment of Congenital and Obligatory Dislocation of the Patella in Children

BACKGROUND

Congenital (fixed) dislocations and obligatory (habitual) patellar dislocations represent a complex clinical and surgical challenge. Numerous treatment options, offering different perspectives, and surgical solutions are reported in the literature.We implemented the surgical technique principles, originally described by Stanisavljevic, for congenital (fixed) and obligatory (habitual) patellar dislocations, with slight modifications.

METHODS

We retrospectively evaluated the results of group of 12 patients (15 knees), operated between the years 2002 and 2013. The procedure includes extensive subperiosteal quadriceps realignment and soft tissue medial plication, followed by distal realignment through patellar tendon splitting. The outcome measures were patellar stability, knee range of motion, Pedi-IKDC knee function score, and the PODCI global function score.

RESULTS

The study group included 12 patients, 9 females and 3 males (15 knees) whose mean age was 5 years 2 months at diagnosis and 7 years 5 months at surgery. Nine patients had an underlying diagnosed genetic background [Down syndrome (n=6), Larsen syndrome (n=2), nail-patella syndrome (n=1)]. The mean follow-up was 46.2 months. Eleven patients, gained stable patella with no recurrence of dislocation. Postoperative knee active extension was improved significantly (P<0.0001) for all patients. The average postoperative Pedi-IKDC and PODCI scores were significantly higher (P<0.001) among the idiopathic group.

CONCLUSIONS

These results suggest that the Stanisavljevic procedure principles with modifications, provides an efficient method for treatment of fixed and obligatory patellar dislocation. In our opinion, young age at surgery played an important role in the surgical outcome.

LEVEL OF EVIDENCE

Level IV-therapeutic.

Early patellar dislocation can lead to tibial tubercle lateralization in rabbits

PURPOSE

To investigate the effects of early patellar dislocation on the tibial tubercle location.

METHODS

Sixty knees from 30 healthy 1-month-old New Zealand white rabbits were randomly divided into two groups of 30 knees each. Group A (control group) comprised the left knees, which underwent no surgical procedures. Group B comprised the right knees, which underwent patellar dislocation surgery. Computed tomography (flexion 0°) was performed preoperatively and 6 months post-operatively. Measurements included the tibial tuberosity-trochlear groove distance (TT-TG) and tibial tubercle lateralization.

RESULTS

No significant difference in the TT-TG or tibial tubercle lateralization was found between the two groups preoperatively. Six months post-operatively, however, the mean TT-TG in Group A (no patellar dislocation) and Group B (patellar dislocation) was 1.0 ± 0.4 and 3.0 ± 0.7 mm, respectively (p < 0.05). The mean tibial tubercle lateralization also showed a significant difference between Groups A and B at 6 months post-operatively (0.5 ± 0.1 and 0.6 ± 0.0, respectively; p < 0.05).

CONCLUSIONS

Early patellar dislocation can lead to tibial tubercle lateralization and an increased TT-TG. Clinically, early intervention for adolescent patients with patellar dislocation will be important.

LEVEL OF EVIDENCE

Prospective comparative study, Level II.

Patella Height Correlates With Trochlear Dysplasia: A Computed Tomography Image Analysis

PURPOSE

The aim of this study was to investigate the position of the patella relative to the trochlea for a possible correlation with radiologic parameters characterizing the form of the trochlea.

METHODS

The computed tomography scans of 36 cases with patellofemoral instability and 30 without (mean age, 24.7 ± 6.8 years) were studied. The height of the patella relative to the trochlea was evaluated as the distance between the axial slice where the patella (P) showed its widest diameter, as the patella at this level has the greatest potential to form the trochlea, and the proximal entrance of the femoral trochlea (TE). The correlations between this parameter and several radiologic parameters used to evaluate trochlear dysplasia, including trochlea height, transverse trochlea shift, trochlea depth, sulcus angle, lateral and medial trochlea slope, trochlea facet asymmetry, and the Dejour trochlea type, were calculated.

RESULTS

The P-TE distance correlated significantly with all trochlea parameters evaluated, with a more dysplastic trochlea in cases of higher position of the patella: medial, central, and lateral trochlea height (0.287 <r < 0.490, P < .019), transverse trochlea shift (r = 0.516, P < .001), trochlea depth (r = -0.299, P = .015), sulcus angle (r = 0.344, P = .005), medial and lateral trochlea slope (-0.274 <r < -0.295, P < .026), trochlea facet asymmetry (r = -0.399, P = .005), and Dejour trochlea type (r = 0.394, P = .001).

CONCLUSIONS

On the basis of our findings it was concluded that patella height was significantly related to the morphology of the femoral trochlea. The strongest correlations with patella height were observed for the parameters central trochlea height (r = 0.490, P < .001) and transverse trochlea shift (r = 0.516, P < .001). A higher positioned patella was associated with a more dysplastic trochlea.

LEVEL OF EVIDENCE

Level III, retrospective cross-sectional study.

Patella morphological alteration after patella instability in growing rabbits

Background

The shape of the patella has been considered to be a predisposing factor resulting in patellar instability, but the effects of abnormal patella position during its development are unclear. The present study evaluated patellar morphological changes after patella instability and evaluated the influence of patellar instability on the patella shape.

Methods

Twenty rabbits that were 2 months old were included in the study. The left knee of each rabbit, defined as the experimental group (N = 20 knees/group), underwent a medial soft tissue restraint release. The right knee of each rabbit, defined as the control group (N = 20 knees/group), did not undergo any surgical procedures. A CT scan was performed on each knee before surgery and 6 months post-surgery to measure the transverse diameter, thickness, Wiberg index, and Wiberg angle for analysis of the patellar morphological changes. Cross-specimen examination was conducted to evaluate the differences between the experimental group and the control group.

Results

The four indices remained the same between the two groups before surgery. However, 6 months after surgery, the mean transverse diameter of the patellae in the experimental group was significantly longer than that in the control group (P < 0.001), while the mean thickness in the experimental group was not significantly greater than that in the control group (P = 0.314), resulting in a flattened shape. The Wiberg indices were not significantly different between the two groups. However, the mean Wiberg angle was higher in the experimental group than in the control group (P < 0.001), which resulted in a flattened articular surface of the patella.

Conclusion

The sectional shape and articular surface of the patella became more flattened after patella instability in this study, which indicates that patella dysplasia could be caused by patella instability. Clinically, early intervention for adolescent patients with patella instability is important.

The patellofemoral joint: from dysplasia to dislocation

Patellofemoral dysplasia is a major predisposing factor for instability of the patellofemoral joint. However, there is no consensus as to whether patellofemoral dysplasia is genetic in origin, caused by imbalanced forces producing maltracking and remodelling of the trochlea during infancy and growth, or due to other unknown and unexplored factors.The biomechanical effects of patellofemoral dysplasia on patellar stability and on surgical procedures have not been fully investigated. Also, different anatomical and demographic risk factors have been suggested, in an attempt to identify the recurrent dislocators. Therefore, a comprehensive evaluation of all the radiographic, MRI and CT parameters can help the clinician to assess patients with primary and recurrent patellar dislocation and guide management.Patellofemoral dysplasia still represents an extremely challenging condition to manage. Its controversial aetiology and its complex biomechanical behaviour continue to pose more questions than answers to the research community, which reflects the lack of universally accepted guidelines for the correct treatment. However, due to the complexity of this condition, an extremely personalised approach should be reserved for each patient, in considering and addressing the anatomical abnormalities responsible for the symptoms. Cite this article: EFORT Open Rev 2017;2. DOI: 10.1302/2058-5241.2.160081. Originally published online at www.efortopenreviews.org.

Femoral trochlear groove development after patellar subluxation and early reduction in growing rabbits

PURPOSE

This animal study aimed to investigate whether early reduction in patellar subluxation could minimize femoral trochlear dysplasia in growing rabbits.

METHODS

Sixty rabbits were divided into four groups (N = 30 knees/group). The control group underwent no surgical procedures. The rabbits in the three experimental groups underwent surgical patellar subluxation. Those in the early-reduced group underwent reduction surgery 1 month after patellar subluxation. The late-reduced group underwent reduction surgery 2 months after patellar subluxation. The rabbits in the non-reduced group underwent no reduction surgery. CT scans were performed monthly to measure the sulcus angle and trochlear width and depth. Gross specimen examination and histological observation were performed to investigate anatomical configuration and changes in the trochlear groove cartilage.

RESULTS

CT scans demonstrated significant differences in the sulcus angle, trochlear width and trochlear depth by 6 months after subluxation surgery in the late-reduced and non-reduced groups. No obvious differences in these parameters were seen in the early-reduced group compared with the control group. Gross specimen examination and histological investigations showed degenerative changes in the femoral trochlear groove and cartilage by 6 months after subluxation surgery in the late-reduced and non-reduced groups. No degenerative changes were found in the early-reduced group, compared with the control group.

CONCLUSION

Our results indicate that patellar subluxation or dislocation early in an animal's development can lead to femoral trochlear dysplasia or flattening and that early relocation of the patella can prevent femoral trochlear dysplasia in growing rabbits.

Does form follow function in trochlear dysplasia? Case report of patellar instability in a below-knee amputee

INTRODUCTION

Patellar instability can be considered as a rapidly increasing musculoskeletal subject of interest. It is now well accepted that multiple factors can produce this pathological condition, isolated, but more often in concert. One major static compound is found to be in trochlear dysplasia. It has been stated that the form of the trochlear surface is primary and genetically bilaterally determined already before use. According to these data, recurrent dislocation of the patella has been described as a hereditary disease with autosomal dominant transmission. Against this assumption, we hypothesize that subjects may devise a flattened trochlea when there is no significant biomechanical interplay and thus input between the patella and the distal femur during developmental growth; according to the assumption form follows function.

PRESENTATION OF CASE

In this context, we report the case of a 16-year old male who previously suffered from a traumatic patellar dislocation during sporting activity in his below-knee amputated lower extremity, which occured at age of 18 months. The patient was allocated with a high-grade trochlear dysplasia in his previously amputated limb, while presenting a normal trochlear shape at his healthy contralateral leg.

DISCUSSION

This rare case therefore reprents the history of an individuum with identic genetic predisposition and different biomechanical influences during childhood, which makes it of high clinical interest. In presence of trochlear dysplasia the patient suffered reluxation and concurrent subjective instability on the lower limb affected by the amputation which was treated with medial patellofemoral ligament (MPFL) plasty using an autologous gracilis graft.

CONCLUSION

One has to consider that a certain biomechanical input may be required for the development of a physiologic trochlear groove.