Risk Factors For Patellar Dislocation Research Articles

Local torsion of distal femur is a risk factor for patellar dislocation

PurposeIt has been widely reported that femoral anteversion is a risk factor for patellar dislocation. This study aims to evaluate whether internal torsion of the distal femur is noticeable in patients without increased femoral anteversion and to assess whether it is a risk factor for patellar dislocation.MethodsA retrospective analysis was conducted on 35 patients (24 females, 11 males) with recurrent patellar dislocation but without increased femoral anteversion treated in our hospital from January 2019 to August 2020. All patients underwent knee X-rays, digital radiography of lower-limbs, and CT scans of hip, knee, and ankle joints to measure femoral anteversion angle, distal femoral torsion angle, TT–TG and Caton-Deschamps index. Thirty-five control cases were matched on age and sex to compare the difference of anatomic parameters between the two groups, and the logistic analysis was used to analyze risk factors for patellar dislocation. Perman correlation coefficient was used to evaluate the correlation among femoral anteversion, distal femoral torsion and TT–TG.ResultsGreater distal femoral torsion was still observed in patients with patellar dislocation but without increased femoral anteversion. The torsion angle of distal femur, TT–TG distance and incidence of Patella Alta in patients with patellar dislocation were greater than those in control group, and the inter-group differences were statistically significant (P < 0.05). The torsion angle of distal femur (OR = 2.848, P < 0.001), TT–TG distance (OR = 1.163, P = 0.021) and Patella Alta (OR = 3.545, P = 0.034) were risk factors for patellar dislocation. However, no significant correlation was found among femoral anteversion, distal femoral torsion and TT–TG in patients with patellar dislocation.ConclusionOn the condition that femoral anteversion did not increase, increased distal femoral torsion was commonly observed in patients with patellar dislocation, which represents an independent risk factor for patellar dislocation.

Fibular hemimelia and risk of patellar dislocations: A case series.

The likelihood of patellar instability and consequently, risk of patellar dislocations is higher in those with anatomical abnormalities. Fibular hemimelia is a congenital disorder resulting in partial or full absence of the fibula, often with absence of the lateral and cruciate ligaments, although this patient group rarely undergoes ligament reconstruction. There is potential for adverse outcomes, in the longer term, including, possible increased risk of patellar dislocation and pain in the knee and hip. We aim to investigate the potential risk of spontaneous, unprovoked patellar dislocation among patients with fibular hemimelia, through a review of medical records and radiological investigations. All patients with a diagnosis of fibular hemimelia were included (n = 25), regardless of ultimate approach to management. Tibiofemoral angle measurement and Caton-Deschamps indices were calculated where suitable radiology was available, to better establish extent of potential patellar instability. All the patients with normal Caton-Deschamps indices had only partial fibular absence, although this does not detract from absence or hypoplasia of the anterior cruciate ligament, as a risk factor for patellar dislocation by predisposing to anterior tibial translation. Notably, of the three patients with increased Caton-Deschamps indices, two had complete fibular absence and underwent definitive amputation surgery at age 18 months and 3 years, respectively. Ultimately, this was a young patient group and on-going follow-up might yield better understanding of knee stability. Maintaining a well-aligned lower limb throughout growth might be protective even in the presence of anatomical abnormalities. This article mainly aims to raise awareness among prosthetic and orthotic professionals regarding the increased risk of patella dislocations.

BONE SHAPE FEATURE CHANGES IN SINGLE AND RECURRENT PATELLAR DISLOCATIONS

Purpose: Patellar dislocation is a traumatic injury involving severe twisting of a knee that may cause significant functional impairment to a young, active patient population. More than 30% of patients experience continued knee instability following conservative treatment, leading to an 8 times higher risk of developing post-traumatic osteoarthritis (PTOA). Moreover, a recurrent dislocation further increases the risk of PTOA by a factor of 4.5. Although some anatomical features have been identified as risk factors for patellar dislocation, few studies have investigated the differences in bone shape between patients with single dislocation and those with recurrent ones.

The risk of osteochondral fracture after patellar dislocation is related to patellofemoral anatomy

Despite the comprehensive literature on the anatomical risk factors for patellar dislocation, knowledge on the risk factors for subsequent osteochondral fracture (OCF) remains limited. Magnetic resonance imaging was used to compare measures of patellofemoral anatomy in patients with OCF after patellar dislocation and propensity score matched patients without OCF. For differing measures, limit values showing a 50% probability for the occurrence of OCF were calculated using predictive logistic regression modelling. Proportions of abnormal measures in the groups were compared using Chi-square test. The association of anatomical measures with OCF location was examined by comparing subgroup mean values in the different OCF locations. Propensity score matching provided a total of 111 matched pairs of patients with OCF and patients without OCF. The patients with and without OCF differed in patellotrochlear index (PTI; 0.54 [95% CI 0.52-0.57] vs. 0.47 [95% CI 0.45-0.49]; p < 0.001), tibial tubercle-posterior cruciate ligament distance (TT-PCL; 21.6mm [95% CI 21.0-22.3mm] vs. 20.5mm [95% CI 20.0-21.1mm]; p = 0.013), trochlear depth (2.5mm [95% CI 2.3-2.7mm] vs. 3.0mm [95% CI 2.8-3.2mm]; p < 0.001) trochlear facet asymmetry ratio (0.54 [95% CI 0.51-0.57] vs. 0.43 [95% CI 0.42-0.45]; p < 0.001) and trochlear condyle asymmetry ratio (1.04 [95% CI 1.03-1.04] vs. 1.05 [95% CI 1.04-1.05]; 0.013. Thresholds for increased OCF risk were > 0.51 for PTI > 21.1mm for TT-PCL < 2.8mm for trochlear depth > 0.48 for trochlear facet asymmetry ratio and < 1.04 for trochlear condyle asymmetry ratio. In patients with OCF after patellar dislocation, trochlear configuration and patella vertical location were closer to normal anatomy, whereas patella lateralization was more severe when compared to patients without OCF. These anatomical factors contribute to the risk of OCF during patellar dislocation. III.

Hindlimb torsional alignment changes in growing rabbits after patellar dislocation

BackgroundTorsional 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.MethodsIn 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.ResultsAfter 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).ConclusionsFrom 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.

Trochlear Morphology Development: Study of Normal Pediatric Knee MRIs.

Trochlear dysplasia is a known risk factor for patellar dislocations yet normal trochlea development is not well described. This study will define the articular cartilage (AC) and subchondral trochlear morphology development in pediatric patients using magnetic resonance imaging (MRI) evaluation. A retrospective knee MRI review included patients aged 3 to 16 years with nonpatellofemoral-related diagnoses. International classification of diseases-9/International classification of diseases-10 codes were used to identify eligible study patients. Measurements of the trochlea were made on the basis of previously established methods using the axial MRI just distal to the physis at the deepest portion of the trochlear groove. Three linear [lateral trochlear height (LTH), medial trochlear height (MTH), and central trochlear height (CTH)] and 3 angular [sulcus angle (SA), lateral trochlear slope (LTS), and medial trochlear slope (MTS)] were made at AC and subchondral bone (SCB). The 12 measurements were made independently by 2 study authors. Inter-rater reliability was assessed using an interclass correlation coefficient for absolute agreement to the average of the scores. Trochlea measurements were summarized across age quartiles defined as first quartile (age, 5.1 to 8.3 y), second quartile (8.3 to 11.5 y), third quartile (11.5 to 14.3 y), fourth quartile (14.3to 16.9 y). Associations between age and trochlea measures were assessed using linear regression with Huber-White-adjusted SEs to account for clustering from a small number of patients (N=16) with >1 MRI. In total, 246 knee MRIs from 230 patients were included in this study; 113 patients (51%) were female, whereas 117 (49%) were male. A total of 116 MRIs (47%) were of the left knee and 130 (53%) were right knee. The average patient age was 11.4±3.4 years. Inter-rater agreement was high across all measures with interclass correlation coefficient values >0.7. Mean values for measurements are presented by age quartiles. LTH, MTH, and CTH showed a linear increase with age (range, 2 to 2.6 cm/y; P<0.001). SA, LTS, MTS measured at AC showed no change with age (P>0.05); however, LTS and MTS measured at SCB showed significant increases with age (0.6 and 0.9 degrees/y; P<0.001), whereas SA showed a decrease with age (-1.4 degrees/y; P<0.001). There were no significant differences found in the age associations by laterality, left versus right. There were no sex differences in the age associations for SA, LTS (P>0.05); however, for MTH, LTH, and CTH, males were found to have a significantly greater growth rate (P<0.001). This study found an increase in AC and SCB MTH, LTH, and CTH over time, as well as an increase in SCB LTS and MTS, with a decrease in SA. However, AC of the LTS and SA remained constant, with no significant change throughout growth. This normative data indicate that the LTS and SA of AC are predictors of final trochlea shape in normal development. Final trochlear morphologic development is nearly complete around age 12 years, with no significant changes occurring thereafter.

Femoral derotation osteotomy for recurrent patellar dislocation.

Excessive femoral internal torsion is an important risk factor for patellar dislocation. The aim of the present study was to estimate the effect of derotational osteotomy of the femur on the tibial tubercle trochlear groove (TTTG) distance or patellar tilt angle (PTA) and to report our clinical outcomes of recurrent patellar dislocation after femoral derotation osteotomy. A retrospective analysis of 16 patients (17 knees) with recurrent patellar dislocation treated by femoral derotation osteotomy in our department from January 2016 to February 2019 was carried out. The procedure was performed with supracondylar femoral derotation. A few procedures were combined with soft tissue procedures. Knee function was evaluated by using the International Knee Documentation Committee (IKDC) score, Kujala score, Lysholm score, visual analog scale (VAS) score and patient satisfaction. Additionally, CT was used to assess the influence of femoral derotational osteotomy on TTTG distance and PTA. The average femoral antetorsion angle before surgery was 33° (SD ± 5°), and the intraoperative correction angle was 23° (SD ± 4°). A total of 17 femoral derotation osteotomies in 16 patients with patellar instability [11 females, 5 males, aged 20.8 (range 15-41) years] were included in the study. No dislocation occurred within 26.5months after follow-up (range 12-49months). The IKDC score, Kujala score, Lysholm score and VAS score significantly improved. The preoperative TTTG distance was 15.63mm (SD ± 2.07mm), and it was 14.69mm (SD ± 1.78mm) at the follow-up. The PTA decreased from 26.35° (SD ± 6.86°) to 11.65° (SD ± 2.85°). The powers of TTTG and PTA measurements are 0.78 and 1.00, respectively and all of these differences were statistically significant. Derotational osteotomy of the femur for the treatment of recurrent patellar dislocation can achieve good clinical results, including improved TTTG distance and PTA and improved knee function.

Surgery for patellar dislocation has evolved towards anatomical reconstructions with assessment and treatment of anatomical risk factors

PurposeIncreasing knowledge on the treatment of patellar dislocation has resulted in the development of new surgical techniques for patella stabilisation. National incidence and trends in surgery for patellar dislocation were examined using data from the Finnish National Hospital Discharge Register (NHDR). The hypothesis was that an increased understanding of the pathophysiology of patellar instability has increased the popularity of reconstructing damaged structures and modification of anatomical risk factors.MethodsData from the years 1997–2016 were collected from the NHDR database using ICD-10 diagnostic codes and the Nomesco Classification of Surgical Procedures (NCSP) codes. Surgical procedures were categorised into subgroups representing the main surgical approaches of patellar dislocation. Total incidence of surgery for patellar dislocation and change in incidence during the study period were calculated.ResultsA total of 9702 operations for patellar dislocation were performed during the study period. Median (IQR) patient age at time of primary surgery was 23 (18–34) years. The total incidence of surgeries remained stable across the study period at of 8.9 per 100,000 person-years. Incidences of ligament reconstruction, femoral osteotomies and osteochondral fragment reimplantation operations multiplied during the study period. Ligament reconstruction procedures were the most performed operations at the end of the study period.ConclusionThe incidence of surgical procedures for patellar dislocation remained unchanged during the years 1997–2016. Ligament reconstruction procedures increased in popularity. Surgical techniques have shifted towards the reconstruction of damaged structures and the modification of congenital anatomical risk factors for patellar dislocation. Diversified surgical techniques have enabled the tailoring and combining of stabilizing procedures according to the patient’s individual anatomy.

Anatomical Risk Factors for Anterior Cruciate Ligament Injury Are Not Important As Patellar Instability Risk Factors in Patients with Acute Knee Injury.

To compare in magnetic resonance imaging the anatomical risk factors for anterior cruciate ligament (ACL) injury and patellar dislocation among patients who suffered acute knee injury, 105 patients with acute knee injury resulting in 38 patellar dislocations (patella group), 35 ACL injuries (ACL group), and 32 meniscus or medial collateral ligament injuries (control group) were included. These groups were compared for risk factors for patellar dislocation (patellar height, trochlear dysplasia, and quadriceps angle of action) and for ACL injury (intercondylar width, posterior inclination of tibial plateaus, and depth of the medial plateau). Univariate analysis found statistically significant differences (p < 0.05) between the patella and ACL groups in patellar height (Caton-Deschamps [CD] 1.23 vs. 1.07), trochlear facet asymmetry (55 vs. 68%), PTTG (13.08 vs. 8.01 mm), and the patellar tip and trochlear groove (PTTG) angle (29.5 vs. 13.71 degrees). The patella group also differed from control in medial plateau inclination (4.8 vs. 1.87 degrees), patellar height (CD 1.23 vs 1.08), trochlear facet asymmetry (55 vs. 69%), lateral trochlear inclination (17.11 vs. 20.65 degrees), trochlear depth (4.1 vs. 6.05 mm), PTTG (13.08 vs. 9.85 mm), and the PTTG angle (29.5 vs. 17.88 degrees). The ACL and control groups were similar in all measures. Multivariate analysis found the following significant determinants between the Patella and Control groups: patellar height (CD index, odds ratio [OR]: 80.13, p = 0.015), trochlear anatomy (asymmetry of facets M/L, OR: 1.06, p = 0.031) and quadriceps action angle (PTTG angle, OR: 1.09, p = 0.016); between the ACL and control groups: PTTG angle (OR: 0.936, p = 0.04) and female gender (OR: 3.876, p = 0.032); and between the patella and ACL groups, the CD index (OR: 67.62, p = 0.026), asymmetry of the M/L facets (OR: 1.07, p = 0.011) and PTTG angle (OR: 1.16, p < 0.001). In conclusion, in patients with acute knee injury, the anatomical factors patellar height, trochlear dysplasia, and quadriceps angle of action were related to the occurrence of patellar dislocation. None of the anatomical factors studied was related to the occurrence of anterior cruciate ligament injury.

TROCHLEAR MORPHOLOGY DEVELOPMENT: STUDY OF NORMAL PEDIATRIC KNEE MRIS

Introduction:Trochlear dysplasia is a known risk factor for patellar dislocations yet normal trochlea development is not well described. This study will define the articular cartilage and subchondral trochlear morphology development in pediatric patients using MRI evaluation.Methods:Retrospective knee MRI review including patients aged 3-16 years with non-patellofemoral related diagnoses. ICD-9/ICD-10 codes identified eligible study patients. Measurements of the trochlea were made based on previously established methods using the axial MRI image just distal to the physis at the deepest portion of the trochlear groove. Three linear (Lateral Trochlear Height (LTH), Medial Trochlear Height (MTH), Central Trochlear Height (CTH)) and three angular (Sulcus Angle (SA), Lateral Trochlear Slope (LTS), Medial Trochlear Slope (MTS)) were made at the Articular Cartilage (AC) and Subchondral Bone (SCB) (Figure 1). Twelve measurements were made independently by two study authors. Interrater reliability was assessed. Trochlea measurements were summarized across age quartiles: 1st (age 5.1 - 8.3y), 2nd (8.3 - 11.5y), 3rd (11.5 - 14.3y), 4th (14.3 - 16.9y). Associations between age and trochlea measures were assessed using linear regression with Huber-White adjusted standard errors.Results:246 knee MRIs from 230 patients were included in this study. 113 patients (51%) were female while 117 (49%) were male. 116 MRIs (47%) were of the Left knee and 130 (53%) were Right knee. Average patient age was 11.4±3.4 years. Interrater agreement was high (ICC values >0.7). Mean values for measurements are presented by age quartiles (Table 1). LTH, MTH, and CTH showed linear increase with age (range 2 to 2.6 mm per year, p<0.001). SA, LTS, MTS measured at the AC showed no change with age (p>0.05) however LTS and MTS measured at SCB showed significant increases with age (0.6 and 0.9 degrees per year, p<0.001) while SA showed a decrease with age (-1.4 degrees per year, p<0.001). There were no significant differences found in the age associations by laterality, left vs right. There were no gender differences in the age associations for SA, LTS, MTS (p>0.05) however for MTH, LTH, and CTH, males were found to have a significantly greater growth rate (p<0.001).Conclusions:This study found an increase in articular cartilage and subchondral bone MTH, LTH, and CTH over time as well as an increase in subchondral bone LTS, MTS, and SA. However, no significant change in articular cartilage LTS, MTS, or SA was found. This normative data indicates that articular cartilage angles determine final trochlear morphology.Table 1.Descriptions of Trochlea measures across age quartilesOutcome1st Quartile (age 5.1 - 8.3) (N) Mean ± SD2nd Quartile (age 8.3 - 11.5) (N) Mean ± SD3rd Quartile (age 11.5 - 14.3) (N) Mean ± SD4th Quartile (age 14.3 - 16.9) (N) Mean ± SDLateral Trochlear Height (AC)(62) 48.5 ± 5.0(61) 57.7 ± 5.2(62) 65.0 ± 5.4(60) 66.9 ± 5.2Lateral Trochlear Height (SCB)(62) 42.2 ± 5.2(61) 52.6 ± 4.9(62) 61.5 ± 5.5(60) 63.7 ± 6.2Medial Trochlear Height (AC)(62) 46.4 ± 5.1(61) 59.1 ± 29.0(62) 62.7 ± 5.0(61) 64.3 ± 5.2Medial Trochlear Height (SCB)(62) 42.0 ± 5.1(61) 51.8 ± 4.9(62) 59.9 ± 5.0(61) 62.2 ± 5.1Central Trochlear Height (AC)(62) 43.4 ± 4.7(61) 51.8 ± 4.8(62) 59.1 ± 5.1(61) 60.8 ± 4.9Central Trochlear Height (SCB)(62) 39.1 ± 4.6(61) 47.2 ± 4.4(62) 55.2 ± 5.2(61) 57.1 ± 4.5Sulcus Angle (AC)(62) 145 ± 7(61) 142 ± 7(62) 142 ± 10(61) 145 ± 7Sulcus Angle (SCB)(62) 151 ± 8(61) 142 ± 6(62) 138 ± 10(61) 139 ± 8Difference in Sulcus Angle (SCB - AC)(62) 5.63 ± 7.27(61) 0.03 ± 5.79(62) -4.2 ± 13.1(61) -5.83 ± 5.24Lateral Trochlear Slope (AC)(62) 19.0 ± 3.9(61) 20.0 ± 3.4(62) 18.9 ± 4.8(61) 18.0 ± 4.6Lateral Trochlear Slope (SCB)(62) 14.4 ± 4.3(61) 18.6 ± 3.5(62) 20.3 ± 5.6(61) 19.3 ± 4.5Medial Trochlear Slope (AC)(62) 15.9 ± 5.2(61) 18.4 ± 5.1(62) 17.9 ± 5.3(61) 17.8 ± 5.3Medial Trochlear Slope (SCB)(62) 15.0 ± 5.2(61) 19.8 ± 5.0(62) 22.2 ± 5.6(61) 22.1 ± 5.9Figure 1.Descriptions of MRI measurements on axial MRI

Medial Patellofemoral Ligament Reconstruction: Indications, Technique, and Outcomes

The medial patellofemoral ligament is the primary static restraint to lateral patellar translation. It is injured in 96% to 100% of patellar dislocations that affect approximately 6 to 29 of 100,000 patients and is more common in patients younger than 20 years of age. Risk factors for patellar dislocation include patella alta, trochlear dysplasia, genu valgus, increased Q angle, and hyperlaxity. The treatment for patellar instability depends on the clinical and radiographic findings and can be nonoperative for first-time dislocations (bracing, proximal strengthening, and progressive return to sport) or operative for recurrent dislocations. It is critical for medial patellofemoral ligament reconstruction to reproduce the anatomy and isometry of the native ligament. Graft choice and methods of fixation are less critical to achieve successful outcomes. Studies have reported successful outcomes and improved Kujala scores, with recurrent instability ranging from 1% to 5%. Careful surgical technique can avoid complications, including fracture, graft failure, loss of range of motion, persistent anterior knee pain, medial instability, and recurrent instability. The role of the medial quadriceps tendon femoral ligament also should be considered more in future research.

Lussazioni traumatiche acute di rotula

Acute patellar dislocation is a common knee injury that occurs most often in adolescents, frequently associated with sport and physical activities. Two-thirds of acute patellar dislocations occur in young active patients less than 20 years old. Non-contact knee sprain in flexion and valgus is the leading mechanism for patellar dislocation, accounting for as many as 93% of all cases. The strong displacement of the patella tears the medial stabilizing structures, and mostly the medial patellofemoral ligament (MPFL), which is almost always injured in acute patellar dislocation, most frequently at its femoral attachment. Plain X-ray and CT are mandatory to diagnose bony risk factors for patellar dislocation and plan correction. MRI gives the best information on cartilage and capsulo-ligamentous status for treatment planning: free bodies or osteochondral fracture should be treated surgically. Acute patellar dislocation is associated with a high rate of recurrent patellar instability, instability symptoms and, eventually, patellofemoral osteoarthritis. A consensus on its management is still lacking. Though most authors have reported good results with conservative treatment, a surgical approach would be necessary in the presence of severe cartilage damage or a relevant disruption of the medial stabilizers with instability and subluxation of the patella.

Patellar Dislocation in the United States: Role of Sex, Age, Race, and Athletic Participation

Patellar instability has been extensively studied in selected, high-risk cohorts, but the epidemiology in the general population remains unclear. A longitudinal, prospective epidemiological database was used to determine the incidence and demographic risk factors for patellar dislocations presenting to emergency departments of the United States. The National Electronic Injury Surveillance System was queried for all patellar dislocations presenting to emergency departments between 2003 and 2008. Incidence rate ratios (IRRs) were then calculated with respect to sex, age, and race. The hypothesis was that patellar dislocation is influenced by sex, age, race, and athletic participation. An estimated 40,544 patellar dislocations occurred among an at-risk population of 1,774,210,081 person-years for an incidence rate of 2.29 per 100,000 person-years in the United States. When compared with males, females showed no significant overall or age-stratified differences in the rates of patellar dislocation (IRR 0.85, 95% CI 0.71, 1.00; p = 0.08; p > 0.05). Peak incidence of patellar dislocation occurred between 15 and 19 years of age (11.19/100,000 person-years). When compared with Hispanic race, black and white race were associated with significantly higher rates of patellar dislocation (IRR 4.30 [95% CI 1.63, 6.97; p = 0.02], IRR 4.02 [95% CI 1.06, 6.98; p = 0.03], respectively). Nearly half (51.9%) of all patellar dislocation occurred during athletic activity, with basketball (18.2%), soccer (6.9%), and football (6.3%) associated with the highest percentage of patellar dislocation during athletics. Age between 15 and 19 years is associated with higher rates of patellar dislocation. Sex is not a significant risk factor for patellar dislocation. Black and white race are a significant risk factor for patellar dislocation when compared with Hispanic race. Half of all patellar dislocation occurs during athletic activity. This study was conducted on the Level of evidence II.

Value of the Tibial Tuberosity–Trochlear Groove Distance in Patellar Instability in the Young Athlete

Background A lateralized tibial tubercle may be a relevant anatomic factor in patients with patellar instability and can be used as an indication for a distal realignment procedure. However, parameter values for the tibial tuberosity–trochlear groove (TT-TG) distance in the young patient have not been defined. It also remains to be determined how this parameter contributes to patellar instability in the growing knee joint. Purpose The purpose of this study was to evaluate the value of the TT-TG distance in patellar instability in the young athlete. Study Design Case control study; Level of evidence, 3. Methods Knee magnetic resonance images were collected from 109 patients with lateral patellar instability and from 136 control subjects. Student t test and multiple logistic regression analysis were used to compare the absolute and relative values of the TT-TG distance between patients and controls. The relative value was defined as the ratio between the TT-TG distance and the total width of the distal femur. Results The TT-TG distance (absolute and relative to femur width) differed significantly between patients with patellar dislocation and the control group (both P < .01). The TT-TG distances were on average 4 mm larger in patients with patellar dislocation; TT-TG distance divided by femur width was on average 5% larger in patients with patellar dislocation. Multiple logistic regression analysis confirmed the TT-TG distance as a significant risk factor for patellar dislocation (P = .04), but showed no significant interaction with patient age or femur width (P = .95 and P = .15, respectively). Conclusion A lateralized tibial tubercle is a relevant anatomic factor in the young athlete and in the adult patient with lateral patel-lar instability. Its parameter values and its influence on patellar dislocation are independent of patient age and should therefore be evaluated as in adults.

The association between patella alta and structural features of osteoarthritis on MRI: The Multicenter Osteoarthritis (MOST) Study

Patella alta (PA) is present when the patella position is high relative to the femoral trochlea, and is a known risk factor for patellar dislocation and anterior knee pain in young persons. PA is defined as present when the Insall‐Salvati ratio (ISR), length of the patellar tendon (LT) divided by length of the patella (LP), is = 1.2. The purpose of this study was to determine, in middle aged and older persons at risk for knee osteoarthritis, the association between PA and patellofemoral joint (PFJ) cartilage morphology and bone marrow lesions (BMLs). We measured the ISR on the lateral radiograph in 443 subjects from a cohort study of persons aged 50‐79 years. Cartilage morphology and BMLs were graded on MRI using a semi‐quantitative scale (0‐6, 0‐3 respectively, with 0 representing absence of pathology) in the medial and lateral PFJ. Using logistic regression, we determined the association between the ISR and cartilage morphology and BMLs, adjusting for age, sex, and BMI. The mean ISR was 1.095 and 113 subjects' (26%) ISR was = 1.2. Compared with subjects who did not have PA, those with PA had 1.82 (95% CI 1.26, 2.63) and 2.38 (1.59, 3.58) times the odds of lateral PFJ cartilage damage and BMLs, respectively. We are currently investigating the biomechanical mechanism for the changes seen in bone and cartilage in subjects with PA. This research was supported by the NIH and Arthritis Foundation.Grant Funding SourceNIH and Arthritis Foundation

Revision surgery for patellar dislocation after primary total knee arthroplasty

This study evaluated risk factors for patellar dislocation after primary total knee arthroplasty and determined functional outcomes in patients following revision. Thirty-nine knees in 39 patients averaging 68 years (range, 27–91 years) at the time of revision were evaluated at a mean of 3.2 years (range, 2–7 years). Mean Knee Society and Function scores significantly improved from 34 and 35 to 77 and 54, respectively. Patellar dislocation most commonly resulted from errors in technique such as soft-tissue imbalance and malaligned components that led to poor tracking of the patella. Patellar tracking only improved after soft-tissue realignment in combination with revision of malaligned or loose components. Although revision significantly improved active knee extension and Knee Scores, two thirds of the patients had residual disabilities and pain.