Treatment of patella alta in patients with episodic patellar dislocation: a systematic review

Purpose

While there are numerous anatomic contributors to patellar instability, the role of patella alta has been traditionally under-appreciated. The goal of this systematic review is to identify the described techniques for treating patella alta in skeletally mature patients with episodic patellar dislocation (EPD) and review their published results.

Methods

A comprehensive literature review was performed to identify published surgical techniques and their results. Tibial tubercle distalization is the primary described treatment for patellar alta in patients with EPD, and five studies reporting results of this procedure were reviewed.

Results

Tibial tubercle distalization was generally successful in normalizing patellar height and preventing recurrent patellar dislocation. Physical examination tests for instability such as patellar apprehension remained positive in 15 to 33 % of patients. Patient-reported outcomes were rarely reported and difficult to interpret given the lack of pre-operative values or comparison groups.

Conclusion

Tibial tubercle distalization is an effective technique for correction of patellar height and preventing recurrent patellar dislocations. More comparative studies are required to evaluate patient-reported outcomes of this technique, the effect of an associated tubercle medialization, and the results of supplementing distalization with procedures such as MPFL reconstruction.

Level of evidence

Systematic review of case series, Level IV.     

Development of the femoral trochlear groove in rabbits with patellar malposition

Purpose

The geometry of the trochlear groove is considered to be an important determinant in the pathogenesis of the patellofemoral joint disorders. However, the effect of patellar position during the development of the femoral trochlear groove is unclear. This animal study aimed to investigate the relationship between the position of the patella and development of the femoral trochlear groove in growing rabbits.

Methods

Thirty-two knees from 16 rabbits were included in this study and were divided into two groups. First group consisted of the left knees and was used as a control group with no surgical interventions. The second group involved the right knees on which patellar tendon Z-plasty lengthening was performed to cause patellar malposition (patella alta) before 1 month of age. Computed tomographic (CT) evaluations of both knees were obtained when the animals were 1 month age before the surgical intervention and also at 6 months after the surgical intervention. Angle and depth measurements were acquired from the proximal, middle, and distal reference points along the femoral trochlear groove. After the CT scan acquisition at 6 months following the surgical procedures, rabbits were killed and additional measurements of the trochlear groove angles were performed manually.

Results

The mean middle and distal trochlear groove angles for the experiment group with patella alta were significantly higher compared to that of control group (p < 0.017). The increase in mean trochlear depth for the animals in the control group was found to be significantly higher compared to experiment group at the distal zone (p < 0.017).

Conclusion

Distal femoral groove with an inadequately positioned patella becomes more flattened and this may be a predisposing factor for patellar instability.

Level of evidence

Controlled laboratory study, Level II.     

Prevalence and patterns of anatomical risk factors in patients after patellar dislocation: a case control study using MRI

Objective

To assess anatomical risk factors in patients after lateral patellar dislocation (LPD) and controls using MRI.

Methods

MR images of 186 knees after LPD and of 186 age- and gender-matched controls were analysed. The presence of trochlear dysplasia was assessed by evaluation of trochlear inclination, facet asymmetry, and trochlear depth; patella alta was evaluated by the Insall-Salvati index and Caton-Deschamps index; the lateralised force vector was measured by the tibial tuberosity-trochlear groove (TT-TG) distance.

Results

Compared with controls, dislocators had significantly lower values for all three parameters of trochlear dysplasia (?32 %, ?32 %, ?44 %) and significantly higher values for patella alta (+14 %,+13 %) and TT-TG (+49 %) (all P?<?0.001). Trochlear dysplasia was observed in 112 dislocators (66 %), of whom 61 (36 %) additionally had patella alta and 15 (9 %) an abnormal TT-TG. As isolated risk factors, patella alta (15 %) and abnormal TT-TG (1 %) were rare. Only 25 dislocators (15 %) had no anatomical risk factors. Trochlear dysplasia in conjunction with abnormal TT-TG or patella alta is associated with a 37- and 41-fold higher risk.

Conclusion

Most dislocators have anatomical risk factors, varying in severity and constellation.

Key Points

? Magnetic resonance imaging provides unique information about anatomical variation within the knee. ? Anatomical variants increase the risk for lateral patellar dislocation (LPD) ? Trochlear dysplasia is the main risk factor for LPD. ? Patellar alta and abnormal tibial tuberosity-trochlear groove distance may be additional factors. ? Patient-specific evaluation of risk factors following LPD may help future management.     

Which patellae are likely to redislocate?

Purpose

The purpose of this study was to identify the risk factors for recurrent lateral patellar dislocations and to incorporate those factors into a patellar instability severity score.

Methods

Sixty-one patients [male/female 35/26; median age 19 years (range 9–51 years)] formed the study group for this investigation. Within the study group, 40 patients experienced a patellar redislocation within 24 months after the primary dislocation, whereas 21 patients, who were assessed after a median follow-up of 37 months (range 24–60 months), had not experienced a subsequent episode of lateral patellar instability. In all patients, age at the time of the primary dislocation, gender, the affected body side, body mass index, bilateral instability, physical activity according to Baecke’s questionnaire, the grade of trochlear dysplasia, patellar height, tibial tuberosity–trochlear groove (TT–TG) distance, and patellar tilt were assessed. The odds ratio (OR) of each factor with regard to the patellar redislocation was calculated using contingency tables. Based on these data, a “patellar instability severity score” was calculated.

Results

The patellar instability severity score has six factors: age, bilateral instability, the severity of trochlear dysplasia, patella alta, TT–TG distance, and patellar tilt; the total possible score is seven. Reapplying this score to the study population revealed a median score of 4 points (range 2–7) for those patients with an early episode of patellar redislocation and a median score of 3 points (range 1–6) for those without a redislocation (p = 0.0004). The OR for recurrent dislocations was 4.88 (95 % CI 1.57–15.17) for the patients who scored 4 or more points when compared with the patients who scored 3 or fewer points (p = 0.0064).

Conclusion

Based on the individual patient data, the patellar instability severity score allows an initial risk assessment for experiencing a recurrent patellar dislocation and might help differentiate between responders and non-responders to conservative treatment after primary lateral patellar instability.

Level of evidence

Case–control study, Level III.     

Anatomical factors influencing patellar tracking in the unstable patellofemoral joint

Purpose

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

Methods

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

Results

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

Conclusion

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

Level of evidence

Diagnostic study, Level II.     

Patellar shape can be a predisposing factor in patellar instability

Purpose  

Predisposing factors to objective patellar instability include trochlear dysplasia, patella alta, patellar tilt and elevated tibial tuberosity–femoral groove distance. The shape of the patella is classically not considered a predisposing factor. Anomalies of dynamic and static factors, including excessive patellar height, tibial tubercle lateralisation or trochlear dysplasia, may influence the development of the patella.     

High rate of recurrent patellar dislocation in skeletally immature patients: a long-term population-based study

Purpose

Patellar dislocation can occur in isolation or be associated with chronic instability. The goals of this study are to describe the rate and factors associated with additional patellar instability events (ipsilateral recurrence and contralateral dislocation), as well as the development of patellofemoral arthritis in patients who are skeletally immature at the time of first patellar dislocation.

Methods

The study included a population-based cohort of 232 skeletally immature patients who experienced a first-time lateral patellar dislocation between 1990 and 2010. A chart review was performed to collect information related to the initial injury, treatment, and outcomes. Subjects were followed for a mean of 12.1 years to determine the rate of subsequent patellar dislocation (ipsilateral recurrence or contralateral dislocation) as well as clinically significant patellofemoral arthritis.

Results

104 patients had ipsilateral recurrent patellar dislocation. The cumulative incidence of recurrent dislocation was 11% at 1 year, 21.1% at 2 years, 37.0% at 5 years, 45.1% at 10 years, 54.0% at 15 years, and 54.0% at 20 years. Patella alta (HR 10.6, 95% CI 3.6, 36.1), TT-TG?≥?20 mm (HR 18.7, 95% CI 1.7, 228.2), and trochlear dysplasia (HR 23.7, 95% CI 1.0, 105.2) were associated with recurrence. Similarly, 18 patients (7.8%) had contralateral patellar dislocation. The cumulative incidence of patellofemoral arthritis was 0% at 2 years, 1.0% at 5 years, 2.0% at 10 years, 10.1% at 15 years, 17% at 20 years, and 39.0% at 25 years. Osteochondral injury was associated with arthritis (HR 25.7, 95% CI 6.2, 143.8). There was no association with trochler dysplasia (HR 1.2, 95% CI 0.2, 5.0), recurrent patellar instability (HR 1.2, 95% CI 0.2, 7.2), gender (HR 1.3, 95% CI 0.3, 5.6), or patellar-stabilizing surgery (HR 0.7, 95% CI 0.2, 3.5) and arthritis.

Conclusion

Skeletally immature patients had a high rate of recurrent patellar instability that was associated with structural abnormalities such as patella alta,TT-TG?≥?20 mm, and trochlear dysplasia. Approximately 10% of patients experienced a contralateral dislocation and 20% of patients developed arthritis by 20 years following initial dislocation. Osteochondral injury was associated with arthritis.

Level of evidence

Retrospective case series, Level IV.

     

Influence of age on clinical outcomes of three-dimensional transfer of the tibial tuberosity for patellar instability with patella alta

Purpose

To evaluate the clinical outcomes of three-dimensional (3D) transfer of the tibial tuberosity for patellar instability with patella alta, with a focus on the influence of age at initial surgery.

Methods

Three-dimensional surgery was performed on 28 knees with a mean follow-up of 46 months. Patients were separated into three groups based on the age at initial surgery: group A, 10 knees and an average age of 16.3 ± 1.8 (14–19) years; group B, 10 knees and an average age of 22.1 ± 2.5 (20–28) years; and group C, eight knees and an average age of 44.0 ± 2.2 (40–46) years. Patellofemoral geometry improvement focused on patella alta by determining the Insall–Salvati ratio and Caton–Deschamps index, rotational malalignment by measuring the tibial tubercle–trochlear groove (TT–TG) distance, and lateral patellar subluxation by measuring the patellar tilt. Clinical outcomes were evaluated by the Lysholm and Kujala scores, which were compared before and after surgery. Cartilage degeneration was evaluated by the International Cartilage Repair Society grading system at initial arthroscopy.

Results

The patellar height, TT–TG, and patellar tilt significantly improved in all groups postoperatively (p < 0.05). The Lysholm and Kujala scores also significantly improved postoperatively; however, both scores were lower in group C than in the other groups (p < 0.05). Particularly, pain scores were more severe in group C than in the other groups, and the severity of cartilage degeneration correlated with the pain scores (p < 0.05). Cartilage damage differed significantly between the groups at initial arthroscopy; particularly, group C included grades III and IV cartilage degeneration (p < 0.05).

Conclusions

Age at initial surgery may be the predicting factor for poor clinical outcomes of 3D transfer surgery. The clinical outcome may depend on the age at surgery, which correlated with cartilage damage; thus, surgeons should be given this information when patients are considered undergoing patella surgery.

Level of evidence

Therapeutic case series, Level IV.

     

Medial patellofemoral ligament reconstruction for patellar maltracking following total knee arthroplasty is effective

Purpose

Maltracking of the patella after total knee arthroplasty (TKA) remains a well-recognized problem. The medial patellofemoral ligament (MPFL) has shown to be important for patellar stabilization and reconstructions of the MPFL have already shown excellent functional outcomes for patellar instability of the native knee. Nevertheless, there is only limited literature on using an MPFL reconstruction for correction of patellar maltracking after TKA. In this retrospective study, a consecutive case series was evaluated.

Methods

Between 2007 and 2010, nine patients (nine knees) with anterior knee pain and symptomatic (sub)luxations of the patella after primary or revision TKA were treated by reconstruction of the MPFL in combination with a lateral release. In two cases, an additional tibial tuberosity transfer was performed, due to insufficient per-operative correction. Pre-operative work-up included a CT scan to rule out component malrotation and disorders in limb alignment. Pre- and post-operative patellar displacement and lateral patellar tilt were measured on axial radiographs. Clinical outcome was evaluated using the visual analogue scale (VAS) satisfaction, VAS pain, dislocation rate and Bartlett patella score.

Results

Median patellar displacement improved from 29 mm (0–44) to 0 mm (0–9) post-operatively. Median lateral patellar tilt was 45° (23–62) pre-operative and changed to a median 15° (?3 to 21) post-operative. Median VAS satisfaction was 8 (5–9) and only one patient reported a subluxing feeling afterwards. The Bartlett patella score displayed a diverse picture.

Conclusions

Patellar maltracking after primary or revision TKA without malrotation can effectively be treated by MPFL reconstruction in combination with a lateral release. Only in limited cases, an additional tibial tuberosity transfer is needed.

Level of evidence

IV.     

The clinical and radiological results of individualized surgical treatment depending on pathologic abnormalities in recurrent patellar dislocation: low recurrence rate,but unintended patella baja

Purpose

To evaluate the clinical and radiological outcomes and chondral lesion change using individualized surgery for recurrent patellar dislocation.

Methods

A total of 31 knees with recurrent patellar dislocation underwent surgery depending on individual pathologic abnormalities. Pathologic abnormalities including medial laxity, lateral tightness, increased tibial tuberosity (TT)-to-trochlear groove distance (>20 mm), and patella alta (Caton–Deschamps ratio >1.2) were evaluated in each patient. The abnormalities were corrected through medial patellofemoral ligament reconstruction, TT distalization, TT anteromedialization, and lateral retinacula release. The mean follow-up period was 33 months.

Results

There was one recurrent case (3.2%), requiring additional surgery. The mean Kujala scores were significantly (P = 0.002) improved from 75.8 (SD 12.4) to 84.6 (SD 13.1). Tegner scores were significantly improved from 3.7 (range 1–9) to 5.4 (range 2–9) (P < 0.001), as were and visual analogue scale pain scores from 4.7 (SD 2.5) to 2.6 (SD 2.2) (P = 0.001). Caton–Deschamps ratio was significantly decreased from 1.1 (SD 0.2) to 0.9 (SD 0.1) (P < 0.001), regardless of TT distalization. Chondral lesions of the patella and trochlear groove were improved or maintained in 57.1 and 71.4% of patients, respectively.

Conclusion

Individualized surgery in recurrent patellar dislocation was effective and safe with a low recurrence rate. However, the possibility of unintended patella baja, which might be related to post-operative anterior knee pain, should be considered.

Level of evidence

IV.

     

Influence of tibial slope asymmetry on femoral rotation in patients with lateral patellar instability

Purpose

The geometry of the tibial plateau and its influence on the biomechanics of the tibiofemoral joint has gained increased significance. However, no quantitative data are available regarding the inclination of the medial and lateral tibial slope in patients with patellar instability. It was therefore the purpose of this study to evaluate tibial slope characteristics in patients with patellar dislocations and to assess the biomechanical effect of medial-to-lateral tibial slope asymmetry on lateral patellar instability.

Methods

Medial and lateral tibial slope was measured on knee magnetic resonance images in 107 patients and in 83 controls. The medial-to-lateral tibial slope asymmetry was assessed as the intra-individual difference between the medial and lateral tibial plateau inclination considering severity of trochlear dysplasia. The effect of tibial slope asymmetry on femoral rotation was calculated by means of radian measure.

Results

Severity of trochlear dysplasia was significantly associated with an asymmetric inclination of the tibial plateau. Whereas the medial tibial slope showed identical values between controls and study patients (n.s.), lateral tibial plateau inclination becomes flatter with increasing severity of trochlear dysplasia (p < 0.01). Consequently, the intra-individual tibial slope asymmetry increased steadily (p < 0.01) and increased internal femoral rotation in 20° and 90° of knee flexion angles in patients with severe trochlear dysplasia (p < 0.01). In addition, the extreme values of internal femoral rotation were more pronounced in patients with patellar instability, whereas the extreme values of external femoral rotation were more pronounced in control subjects (p = 0.024).

Conclusion

Data of this study indicate an association between tibial plateau configuration and internal femoral rotation in patients with lateral patellar instability and underlying trochlear dysplasia. Thereby, medial-to-lateral tibial slope asymmetry increased internal femoral rotation during knee flexion and therefore might aggravate the effect of femoral antetorsion in patients with patellar instability.

Level of evidence

III.     

Medial patellotibial ligament (MPTL) reconstruction for patellar instability

Purpose

To evaluate mid-term clinical and radiographic outcomes after an original medial patellotibial ligament reconstruction in patients with patellar dislocation.

Methods

Twenty-nine knees (27 patients, 8 males and 19 females) treated for patellar dislocation with medialization of the patellar tendon medial third combined with medial and lateral release were evaluated clinically and radiographically at a mean follow-up of 6.1 ± 2.5 years. Trochleoplasty was performed in case of severe flat trochlea (6 knees, 21 %). Aetiology of patellofemoral instability was traumatic in 6 (21 %) and atraumatic in 23 (79 %) knees. The mean age at first dislocation was 19.2 ± 10.1 years. WOMAC, subjective and objective IKDC, Kujala, VAS for pain, Tegner activity and EQ-5D scores were used. Anteroposterior, lateral and 30° axial views were performed for radiographic monitoring.

Results

There was a significant improvement of all clinical scores and significant reduction in knee pain. Twenty-four knees (83 %) were normal or nearly normal by objective IKDC score at final follow-up. Radiographs showed a higher incidence of patella alta and flat trochlea in the atraumatic group. Severe signs of patellar osteoarthritis were found in 1 knee (3 %). A higher body mass index (BMI) was correlated with worse pre-operative scores. Four knees (14 %) were considered failures (2 further dislocations, 2 revision surgeries). The overall survival rate at 6 years was 0.811.

Conclusions

The presented techniques produced good clinical and radiographic results at mean 6.1 years follow-up, with 14 % failures. Signs of patellofemoral dysplasia were found in patients with atraumatic patellar dislocation. BMI was related to worse pre-operative clinical status.

Level of evidence

Retrospective study, Level IV.     

Dynamic versus static reconstruction of the medial patellofemoral ligament for recurrent lateral patellar dislocation

Purpose

To compare clinical and radiological outcomes of static and dynamic medial patellofemoral ligament (MPFL) reconstruction techniques.

Methods

In a retrospective, matched-paired, cohort analysis, 30 patients surgically treated for recurrent lateral patellar dislocation were divided into two groups of 15 patients matched for inclusion and exclusion criteria. The static technique group underwent rigid fixation of the gracilis tendon at the anatomic femoral MPFL insertion and the superomedial border of the patella; the dynamic technique group underwent detachment of the gracilis tendon at the pes anserinus with fixation to the proximal medial patellar margin via tunnel transfer obliquely through the patella. Kujala, Lysholm, and Tegner scores; pain level; and pre- and postoperative radiographic changes of patellar height, patellar tilt, and bisect offset were compared.

Results

No significant between-group differences were found in mean Kujala, Tegner, Lysholm, or visual analogue scale scores or radiographic parameters. One case of resubluxation was observed in the dynamic group. All but one patient in each group would have been willing to undergo the procedure again.

Conclusions

Both techniques provided satisfactory short-term outcomes.

Level of evidence

III.     

An analysis of knee anatomic imaging factors associated with primary lateral patellar dislocations

Purpose

Various knee anatomic imaging factors have been historically associated with lateral patellar dislocation. The characterization of these anatomic factors in a primary lateral patellar dislocation population has not been well described. Our purpose was to characterize the spectrum of anatomic factors from slice imaging measurements specific to a population of primary lateral patellar dislocation. A secondary purpose was to stratify these data by sex/skeletal maturity to better detail potential dimorphic characteristics.

Methods

Patients with a history of primary lateral patellar dislocation between 2008 and 2012 were prospectively identified. Ten MRI measurements were analysed with results stratified by sex/skeletal maturity. A ‘4-factor’ analysis was performed to detail the number of ‘excessive’ anatomic factors within a single individual.

Results

This study involved 157 knees (79 M/78 F), and 107 patients were skeletally mature. The measurements demonstrate more anatomic risk factors in this population than historical controls. Patella height and trochlear measurements are the most common ‘dysplastic’ anatomic factors in this population. There were differences based on sex for some patellar height measurements and for TT-TG; there were no differences based on skeletal maturity.

Conclusion

Primary lateral patellar dislocation patients have MRI measurements of knee anatomic factors that are generally more dysplastic than the normal population; however, there is a broad spectrum of anatomic features with no pattern predominating. Characterizing knee anatomic imaging factors in the patient with a primary lateral patellar dislocation is a necessary first step in characterizing the (potential) differences between the primary and recurrent patellar dislocation patient.

Level of evidence

IV.

     

Patellofemoral osteoarthritis after Insall’s proximal realignment for recurrent patellar dislocation

Purpose

The aim of the present study was to retrospectively investigate the development of patellofemoral osteoarthritis after the historical Insall’s proximal realignment for patellar stabilisation in patients with recurrent patellar dislocation. Furthermore, risk factors for recurrent patellar dislocation and for patellofemoral osteoarthritis development were evaluated.

Methods

Forty-two patients underwent patellofemoral stabilising surgery by the historic Insall’s proximal realignment; they were evaluated with a mean follow-up period of 52 months. Plain radiography was used to document osteoarthritic changes by using the Iwano classification. MRIs obtained at the latest follow-up were evaluated for patellofemoral cartilage lesions. Univariate and multivariate logistic regression analyses were performed to evaluate the influence of trochlear dysplasia, tibial tubercle–trochlear groove distance and patellar height on redislocation. Pearson’s χ ² and the Spearman’s correlation tests were used to assess a possible correlation between trochlear dysplasia and patellar dislocation, as well as between instability and development of patellofemoral osteoarthritis.

Results

At the latest follow-up, plain radiographs showed a significant increase in patellofemoral osteoarthritis (grades II–IV according to the Iwano classification) in 18 patients (43 %) compared with 4 patients (10 %) at the time of surgery (P = 0.001). Patellofemoral cartilage lesions (grades II–IV) were detected in 18 patients (43 %) on MRI. Nine patients (21 %) had at least one incidence of redislocation at follow-up. Estimated redislocation-associated risk factors could not be determined. Trochlear dysplasia had a significant impact on patellofemoral osteoarthritis development (P = 0.001), whereas recurrent patellar instability had none (n.s.).

Conclusion

Insall’s proximal realignment technique leads to a significant progression of patellofemoral osteoarthritis. No risk factors for redislocation could be found; however, the presence of trochlear dysplasia did correlate with patellofemoral osteoarthritis.

Level of evidence

IV.     

Clinical and radiological outcome of medial patellofemoral ligament reconstruction with a semitendinosus autograft for patella instability

Background: Recurrent patellar instability is a common problem after dislocation. The medial patellofemoral ligament (MPFL) contributes 40–80% of the total medial restraining forces. This study assessed the clinical and radiological outcome after a follow-up of 4 years after linear MPFL reconstruction using an ipsilateral Semitendinosus tendon autograft. Study design and methods: 15 knees in 12 patients were examined with a mean of 47 months after linear reconstruction of the MPFL at a mean age of 30 years. 3 knees underwent previous surgery. 3 patients had mild trochlear dysplasia grade I or II, according to the classification of Dejour. If preoperative tibial tuberosity-trochlear groove distance (TTTG) was more than 15 mm, patients underwent additional medialisation of the tibial tuberosity (n=8) creating a similar postoperative situation for all patients. All patients were available for a postoperative evaluation, which consisted of a subjective questionnaire, the Kujala score, and the recording of potential patellar redislocation and apprehension. Patellar height and tilt was measured on plain radiographs. Postoperative CT scans were performed in patients with an additional tibial tuberosity-transfer. Results: Postoperatively, one patient reported on recurrent bilateral redislocation. Physical examination however revealed no findings. Three knees presented with persistent patellar apprehension. Thirteen knees had improved subjectively after surgery. The mean Kujala score improved significantly from 55.0 to 85.7 points. The patellar tilt decreased significantly from 11.3° to 9.2°. Four knees had patella alta preoperatively, but only two at the latest follow-up visit. Previous surgery or additional trochlear dysplasia had no influence on the clinical outcome. Conclusion: MPFL reconstruction improves clinical symptoms, reduces the patellar tilt substantially, and may correct patella alta. Additional mild trochlear dysplasia did not compromise the outcome; however, this fact needs further attention in a larger study group.     

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.

     

Is tibial tuberosity–trochlear groove distance an appropriate measure for the identification of knees with patellar instability?

Purpose

Tibial tuberosity–trochlear groove distance (TT–TG) has been regarded as a useful tool for establishing therapeutic choices for patellar instability. Recently, it has been shown that TT–TG negatively correlated with the quadriceps angle, suggesting that if used individually, neither provide a valid measure of instability. This study aimed to compare TT–TG distance between both knees in patients with unilateral instability to assess whether this measurement is a decisive element in the management decisions for patellar instability.

Methods

Sixty-two patients (18 male and 44 female), reporting to a specialist patella clinic for recurrent unilateral patellar instability, were included in the study. Patients underwent bilateral long leg computed tomography scan to determine TT–TG distance in both knees. Tibial TT–TG in symptomatic and asymptomatic knees in the same individual was compared statistically.

Results

Mean TT–TG distance in the symptomatic knee was 16.9 (±4.9) mm, compared to 15.6 (±5.6) mm in the asymptomatic knee. Tibial TT–TG was not significantly different between stable and unstable knees (n.s.).

Conclusions

The lack of difference in TT–TG distance between stable and unstable knees suggests that TT–TG distance alone may not be a decisive element in establishing therapeutic choices for patellar instability. It should, therefore, be interpreted with caution during clinical evaluations.

Level of evidence

II.     

No difference in patellar tracking between symmetrical and asymmetrical femoral component designs in TKA

Purpose

Poor knee extension function after total knee arthroplasty (TKA) is associated with factors including articular geometry and alignment. Femoral trochlear geometry has evolved from symmetrical to become more prominent proximal–laterally, with the groove aligned proximal–lateral to distal–medial. This study in vitro tested the hypothesis that a modern asymmetrical prosthesis would restore patellar tracking and stability to more natural behaviour than an older symmetrical prosthesis.

Methods

Six knees had their patellar tracking measured optically during active knee extension. Medial–lateral force versus displacement stability was measured at fixed angles of knee flexion. The measurements were repeated after inserting each of the symmetrical and asymmetrical TKAs.

Results

Significant differences of patellar lateral displacement stability, compared to normal, were not found at any angle of knee flexion. The patella tracked medial–laterally within 2.5 mm of the natural path with both TKAs. However, for both TKAs near knee extension, the patella was tilted laterally by approximately 6° and was also flexed approximately 8° more than in the natural knee.

Conclusion

The hypothesis was not supported: The more anatomical component design did not provide more anatomical patellar kinematics and stability.     

Patella infera or patellar tendon adherence after high tibial osteotomy

Purpose

Alterations in patellar height after high tibial osteotomy are found in many instances. Fibrosis of the tendon is implicated as the cause of the mechanism of patella lowering. This study aimed to determine the relationship between the position of the patella and the histopathological findings at the patellar tendon after high tibial osteotomy.

Methods

Nineteen knees in seventeen patients who were consecutively hospitalised for implant extraction are studied. All of the patients had previously undergone closing wedge osteotomy by the same surgeon at the same department. The median follow-up time is 15 months (range: 11–35). Five patients who all underwent high tibial osteotomy at the same time are also included in the study as a control group for histopathological evaluation. All of the patients are evaluated radiologically, patellar tendon biopsies are taken during the operation, and histopathological analyses are performed.

Results

The shortening of the patellar tendon is statistically significant (P < 0.05). The severity of the vascularisation, inflammation, and fibrotic change observed at the distal part of the tendon is evident. However, there is no statistically significant correlation between these findings and the degree of shortening.

Conclusions

The shortening of the tendon occurs as a result of adherence in the distal part of the tendon. It would appear that it is this shortening that causes the difficulties encountered during arthroplasty surgery of osteotomy patients, and not patella infera.

Level of evidence

Retrospective study, Level II.