Patients with lateral tracking patella have better pain relief following CT-guided tuberosity transfer than patients with unstable patella

In patients with either lateral tracking patella or unstable patella the pathological lateral position of the tuberosity can be corrected by a medial transfer. This study compared the results of subtle CT-guided correction of the tuberosity for objective unstable patella (n=27) with the results for lateral tracking patella (potential instability) as described by Dejour (n=16). Follow-up was 37 months. CT revealed a pathological lateralization of the tibial tuberosity–trochlear groove greater than 15 mm in 41 knees. These patients underwent medialization of the tibial tuberosity up to 10–12 mm lateral from the trochlear groove, and 28 patients underwent a distalization to normalize the Caton index to 1.0–1.2. Results were evaluated using Cox' method. Patients with objective patellar instability were rated as 11% excellent, 52% good, 33% fair, and 4% poor. All patients became stable except one who had a 6° valgus alignment. Although 96% had improved stability, 33% of the patients still had pain. The patients with lateral tracking patella (potential instability) were rated as 37.5% excellent, 44% good, and 19% fair. The lower proportion of pain relief in patients with unstable patella is likely the result of the cartilage damage experienced by these patients following multiple dislocations. Thus the patient with lateral tracking patella without patella dislocations must be differentiated from the one with unstable patella. Their prognosis in pain relief is better.     

Depth insufficiency of the proximal trochlear groove on lateral radiographs of the knee: relation to patellar dislocation

The depth of the trochlear groove was frequently noted to be insufficient in knees with patellar instability, particularly in the proximal portion of the trochlea. To confirm this observation, the depth of the trochlear groove of the femur was measured on lateral radiographs of 218 knees: 40 knees in 20 asymptomatic subjects, 116 knees in 69 patients undergoing radiography for various symptoms (96 without and 20 with patellar subluxation, determined on axial radiographs), and 62 knees in 34 patients who underwent surgery for recurrent dislocation or subluxation of one or both patellae (40 treated and 22 contralateral knees). In the 40 knees that had been operated on, the proximal trochlear depth (measured 1 cm below the upper limit of the trochlear groove) was 2.74 mm +/- 1.35, in contrast to 5.94 mm +/- 1.74 in the asymptomatic subjects and 5.84 mm +/- 1.53 in the patients with symptoms but no patellar instability. Recognition of depth insufficiency in the proximal portion of the trochlea should prompt a search for patellar instability. Axial views made with 30 degrees of knee flexion and lateral rotation of the leg are particularly helpful.     

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.     

Is there a relationship between anterior knee pain and femoral trochlear dysplasia? Assessment of lateral trochlear inclination by magnetic resonance imaging

It may be very difficult to diagnose the pathology in patients with anterior knee pain. Patients with chronic anterior knee pain have been reviewed for the study. Our aim was to delineate the presence of subtle trochlear dysplasia by measuring lateral trochlear inclination (LTI) in axial magnetic resonance imaging (MRI) scans. While there were 109 knees in the study group with anterior knee pain (AKP), control group consisted of 74 knees without AKP. The LTI measurements were performed at the level of proximal cartilaginous area of trochlear groove in axial scans. The condition was termed to be trochlear dysplasia when LTI was below 11o. Parameters in both groups were statistically analyzed and compared for their association with LTI. There was no significant difference between LTI values of male and female subjects in each group. The mean LTI values in anterior knee pain and control groups were 17.32o and 21.5o, respectively, and the difference was statistically significant (P < 0.05). The ratio of knees with trochlear dysplasia was 16.5% in AKP group, which was only 2.7% in control. In the AKP group, the ratio of trochlear dysplasia was significantly high (P < 0.05). Although trochlear dysplasia has been generally detected in cases with patellar instability, this study revealed that the frequency of this finding in patients with other causes of anterior knee pain was also considerably high. Measurement of lateral trochlear inclination in axial MRI scans with radiologic assessment seems to be a valuable diagnostic criterion, especially in patients in whom etiology of anterior knee pain could not be identified.     

MRI performed on dedicated knee coils is inaccurate for the measurement of tibial tubercle trochlear groove distance

Objective

Tibial tubercle trochlear groove distance (TTD) is a significant factor in patello-femoral instability. Initially described on CT scans with the knee in full extension, the measurement has been validated on MR scans. Dedicated knee MRI coils have subsequently superseded both CT and MRI body coils for knee imaging. However, the knee rests in partial flexion within the dedicated knee coil. The objective of this study is to investigate whether images from dedicated knee MRI coils produce different TTD measurements from MR body coils.

Materials and methods

Thirty-two symptomatic knees (27 patients) had simultaneous knee MR scans performed in both a dedicated knee coil and a body coil. TTD measurements were independently compared to assess whether the coil type used affected TTD.

Results

Patients’ ages ranged from 10 to 27 years (mean 15 years). Mean TTD in the dedicated knee coil (partially flexed knee) was 11.3 mm compared with 19.9 mm in the body coil (that permits full knee extension). The mean difference was 8.6 mm, which was highly significant (p?<?0.0001, unpaired t test). Inter-rater correlation co-efficient was 96 %. Of the knees that recorded a “normal” TTD on the dedicated knee coil, 60–100 % recorded a “pathological” TTD on body coil images, depending on which diagnostic value for “normal” cut-off was used.

Conclusion

This study has identified a highly significant difference in TTD measurement when knees are scanned in a dedicated knee coil with the knee partially flexed, compared with an MR body coil. It is critical for surgeons and radiologists managing patello-femoral instability to appreciate this profound difference. TTD measurement taken from knees scanned in dedicated knee coils may lead to patients being falsely re-assured or erroneously denied surgery.     

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.     

Trochlear osteotomy for patellar instability: satisfactory minimum 2-year results in patients with dysplasia of the trochlea

Trochlear dysplasia is a predisposing factor for recurrent patellar instability. We evaluated the results of an anterior lateral femoral condyle open wedge osteotomy for treating patellar instability. A total of 16 consecutive patients (19 knees) with symptoms of recurrent patellar instability and trochlear dysplasia identified using a true lateral radiograph of the knee underwent an anterior lateral femoral osteotomy. Outcomes were documented at 2 years minimum follow-up using the Lysholm scale, the patellofemoral score, WOMAC score and standard conventional radiographs. In 17 knees, patients reported good improvement in stability (no dislocations) and most patients had a marked improvement in pain and functional scores at follow-up (mean follow-up 51 months). No serious complications occurred. Anterior femoral osteotomy of the lateral condyle appears to be a satisfactory and safe method for treating patients with patellofemoral joint instability caused by trochlea dysplasia. In selected cases this procedure can be used to correct trochlea dysplasia. In our opinion, the key to a successful treatment of patellofemoral instability is to successfully distinguish the anatomic deficiencies and to correct the anatomical abnormality.     

TKA using the subvastus approach and lateral retinacular release in patients with permanent post-traumatic patellar dislocation: a report of two cases

Permanent post-traumatic patellar dislocation is a rare condition, and total knee arthroplasty (TKA) can be performed for osteoarthritic knees with this condition. There have been only a few reports about using the standard medial parapatellar approach and extensive lateral release or extensor mechanism realignment for patients with permanent post-traumatic patellar dislocation. We performed two TKAs with using a subvastus approach and lateral release for osteoarthritic knees with permanent post-traumatic patellar dislocation. The patients were well satisfied with their results. The patellae tracked very well in the femoral trochlear groove throughout the full range of motion after the operations. Bone scans were done 1 year postoperatively on both patients, and the scans showed normal vascularity for the patella.     

Incidence and radiologic predictor of postoperative patellar instability after Fulkerson procedure of the tibial tuberosity for recurrent patellar dislocation

Purpose

Excellent results of anteromedialization of the tibial tuberosity for recurrent patellar dislocation have been reported; however, the contribution of the preoperative anatomic factors to postoperative patellar instability has not been well established. The purpose of this study was to investigate the mid-term results and the incidence of postoperative patellar instability after Fulkerson procedure for recurrent patella dislocation, and to determine the radiologic predictor of the postoperative patellar instability.

Methods

Sixty-two knees of 41 patients underwent Fulkerson procedure with or without lateral retinacular release for recurrent patellar dislocation and were followed-up for 85–155 months. Predisposing anatomic factors for recurrent patellar dislocation were evaluated preoperatively, including valgus knee alignment (femorotibial angle), patella alta (Insall–Salvati ratio), trochlear dysplasia (trochlear depth), lateral patellar displacement (congruence angle) and lateral malposition of the tibial tuberosity (tibial tuberosity-trochlear groove distance). The relationship between the measurements of anatomic factors and postoperative patellar instability, which was defined by the patellar re-dislocation or residual apprehension after surgery, was analyzed.

Results

The Fulkerson score and the Kujala score were significantly improved from the median of 65 (35–80) points and 68 (36–82) points preoperatively to 95 (60–100) points and 92 (57–100) points at the final follow-up, respectively. Three knees (4.8%) experienced postoperative patellar re-dislocation and 4 knees (6.5%) showed the positive apprehension sign at the final follow-up. The statistical analysis showed that the postoperative patellar instability correlated with only patella alta.

Conclusion

Patella alta was the only predictor of postoperative patellar instability after Fulkerson procedure. These results indicated that isolated Fulkerson procedure should not be indicated for recurrent patellar dislocation with severe patella alta.

Level of evidence

Case–control study, Level III.     

CT determination of tibial tubercle lateralization in patients presenting with anterior knee pain

Anterior knee pain is commonly associated with patellofemoral malalignment. Both conventional radiographic measurements and CT measurements have been proposed to define and confirm the sometimes difficult clinical diagnosis of anterior knee pain secondary to patellofemoral malalignment. Using CT imaging with computerized technique to measure anatomic relationships, we evaluated patients (n=50) with anterior knee pain for excessive lateralization of the tibial tubercle. The symptomatic knee of each patient was compared with their asymptomatic knee as well as with the knees of patients with other causes of anterior knee pain (n=10) and with the knees of asymptomatic controls (n=10). The symptomatic knee of patients with suspected patellofemoral malalignment demonstrated significantly greater lateralization of the tibial tubercle (12.2±0.5 mm) than did the asymptomatic knee (9.0±0.7 mm). The symptomatic knees of patients with patellofemoral malalignment also demonstrated significantly greater lateralization of the tibial tubercle than did the knees of patients with other causes of anterior knee pain (5.9±0.9 mm). When a control population was added to the analysis, the patients with symptomatic patellofemoral malalignment demonstrated significantly greater lateralization of the tibial tubercle than did the controls (6.4±0.4 mm). Using a critical value of 9 mm lateralization, the CT diagnosis of patellofemoral malalignment had a specificity of 95% and a sensitivity of 85%. We conclude that CT determination of tibial tubercle position assists the diagnosis of patellofemoral malalignment.     

Proximal patellar tendinosis and abnormalities of patellar tracking

Objective. To assess whether an association exists between patellar tendinosis and abnormal patellar tracking. Design and patients. The MRI examinations of 630 patients (i.e. 860 knees) referred with anterior knee pain over a 4-year period were assessed in retrospect for the presence of patellar tendinosis and abnormal patellar tracking. The images of the patients with patellar tendinosis were reviewed and the location within the patellar tendon was recorded. Results. There were 44 knees with proximal patellar tendinosis. Twenty-four of these were considered to have normal patellar tracking and 20 to have abnormal patellar tracking. In the group of 816 knees without proximal patellar tendinosis, 581 were considered to have normal patellar tracking and 235 knees to have abnormal patellar tracking. When the two groups were compared there was a statistically significant difference in the ratio of patients with and without abnormal tracking. Conclusion. In patients referred with anterior knee pain or suspected abnormal patellar tracking there is a significant association between proximal patellar tendinosis and abnormal patellar tracking. Received: 3 June 1998 Revision requested: 4 August 1998; 16 November 1998 Revision received: 9 November 1998; 18 January 1999 Accepted: 29 January 1999     

The relationship between quadriceps angle and tibial tuberosity–trochlear groove distance in patients with patellar instability

Purpose

The quadriceps angle (Q-angle) represents the angle between the vector of action of the quadriceps and the patellar tendon. An increased Q-angle has been associated with an increased risk of patellar instability, although there is disagreement on its reliability and validity as it is affected by the position of the limb and contraction of the quadriceps. Tibial tuberosity?Ctrochlear groove distance (TT?CTG) is ascertained by axial CT scanning, with an increased value associated with patellar instability. This study aimed to determine whether the Q-angle correlates with the TT?CTG distance in patients with patellar instability.

Methods

Q-angles were measured in 34 knees that had previously undergone CT scanning for assessment of patellar instability. Measurements were made with the patient supine, the knee extended and the lower limbs in neutral rotation with the quadriceps relaxed and contracted. TT?CTG distance was measured on CT scanning in an identical position.

Results

Of the 34 knees measured, 24 had symptoms of patellar instability, and 10 were normal. A significant negative correlation between relaxed Q-angle and TT?CTG in all knees was demonstrated (p?=?0.028). In symptomatic knees, contracted Q-angle also demonstrated a significant negative correlation with TT?CTG (p?=?0.037).

Conclusions

If TT?CTG distance is regarded as the gold standard measurement, Q-angle is not a reliable indicator of patellar instability. There is a clear need to develop methods to more fully characterise the knee and factors contributing to patellar instability.

Level of evidence

II.     

Objective patellar instability: MR-based quantitative assessment of potentially associated anatomical features

To evaluate and compare the diagnostic utility of multiple quantitative parameters as measured on knee magnetic resonance (MR) examinations of patients suffering objective patellar instability (OPI). We performed a retrospective evaluation of knee MR examinations in a group of 46 patients (59 knees) with clinically proven OPI, and in a control group of 69 patients (71 knees). Multiple quantitative parameters in both groups were statistically evaluated and compared for their association with OPI. OPI patients tend to present shallower trochlear groove (<5 mm), larger Insall-Salvati index (>1.2), shorter patellar nose (<9 mm), smaller morphology ratio (<1.2), and larger patellar tilt (>11°) than control patients. The best sensitivities were those of the lateral patellar tilt (92.7%), the trochlear groove depth at the roman arch level (85.7%) and the Insall-Salvati index (78%). The best specificities were those of the morphology ratio (86.9%), the patellar nose (84.5%) and the patellar tendon length (84.5%). Shallow trochlear groove may be confidently identified at the roman arch view in OPI patients. Patella alta may be more reliably detected by the Insall-Salvati index in OPI patients. Patellar nose and morphology ratio are very specific indicators of OPI. A short patellar nose (that is to say, a patellar nose ratio of <0.25) has a high association with OPI. Lateral patellar tilt remains the single feature with the highest sensitivity and specificity for identifying OPI patients.The investigation was performed at: Hospital Universitari de Tarragona Joan XXIII, Tarragona, Spain, and Hôpital de la Croix-Rousse, Centre Livet, Caluire, FrancePresented as a scientific paper (731) at the RSNA 2003, original research     

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 dislocations in children, adolescents and adults: A comparative MRI study of medial patellofemoral ligament injury patterns and trochlear groove anatomy

Purpose

The first aim was to compare medial patellofemoral ligament injury patterns in children and adolescents after first-time lateral patellar dislocations with the injury patterns in adults. The second aim was to evaluate the trochlear groove anatomy at different developmental stages of the growing knee joint.

Materials and methods

Knee magnetic resonance (MR) images were collected from 22 patients after first-time patellar dislocations. The patients were aged 14.2 years (a range of 11-15 years). The injury pattern of the medial patellofemoral ligament was analysed, and trochlear dysplasia was evaluated with regard to sulcus angle, trochlear depth and trochlear asymmetry. The control data consisted of MR images from 21 adult patients who were treated for first-time lateral patellar dislocation.

Results

After patellar dislocation, injury to the medial patellofemoral ligament was found in 90.2% of the children and in 100% of the adult patients. Injury patterns of the medial patellofemoral ligament were similar between the study group and the control group with regard to injury at the patellar attachment site (Type I), to the midsubstance (Type II) and to injury at the femoral origin (Type III) (all p > 0.05). Combined lesions (Type IV) were significantly less frequently observed in adults when compared to the study group (p = 0.02). The magnitude of trochlear dysplasia was similar in children, adolescents and adults with regard to all three of the measured parameter-values (all p > 0.05). In addition, the articular cartilage had a significant effect on the distal femur geometry in both paediatrics and adults.

Conclusion

First, the data from our study indicated that the paediatric medial patellofemoral ligament injury patterns, as seen on MR images, were similar to those in adults. Second, the trochlear groove anatomy and the magnitude of trochlear dysplasia, respectively, did not differ between adults and paediatrics with patellar instability. Thus, physicians are confronted with similar anatomical risk factors and similar injuries to the medial soft-tissue restraints in children when compared to adults with patellar instability.     

Patellar tendinopathy with intratendinous alteration on MRI may be related to patellofemoral dysplasia

Patellar tendinopathy (PT ) is a frequent overuse injury of the extensor knee apparatus, whereas as up to 30% of the athletes might suffer from persisting symptoms during their entire career. In the present case‐control study, 47 patients (30.8 ± 11.4 years) with PT with intratendinous alteration (PT ita) of a minimum of ≥25% of the axial surface on MRI and minimum Blazina score of II (pain during without limiting sports activity) were included; MR images were analyzed for trochlear geometry, patellar height/tilt, and tibial tubercle‐trochlear groove distance (TT ‐TG ). The control group (CG ) comprised 87 age‐ and gender‐matched patients without history of anterior knee pain or lateral patellar instability. It was hypothesized that patients with PT might be related to patellofemoral dysplasia. It was found that the patella was significantly higher in patients with PT compared to the CG (patellotrochlear index [PT ‐I]: 0.33 vs 0.37, P  = .014; Insall‐Salvati index [InSa]: 1.18 vs 1.07, P  = .004). PT ‐I was above the cut‐off value in 10.6% of PT knees (CG 5.7%, P  = .27), and InSa in 42.6% (CG 21.8%, P  = .012). TT ‐TG was significantly higher in patients with PT compared to CG (12.0 mm vs 9.9 mm, P  = .002); however, TT ‐TG was only pathologic (>20 mm) in one patient. The trochlear facet ratio was above the cut‐off value in 55.3% of PT patients and 23% of CG (P  < .001), and was significantly greater in patients with PT (0.39 ± 0.09) than CG (0.48 ± 0.1, P  < .001). Knees with PT have significantly more morphological characteristics of patellofemoral instability, which needs to be considered especially in recurrent or treatment‐refractive cases.     

CT changes after trochleoplasty for symptomatic trochlear dysplasia

Trochlear dysplasia is an important risk factor for patellar instability. Because of a decreased trochlear depth in combination with a low lateral femoral condyle, the patella cannot engage properly in the trochlea. Trochleoplasty is a surgical procedure, which strives to correct such bony abnormalities. The aim of this study was to describe morphological features of trochlear dysplasia and the corrective changes after trochleoplasty on CT scan. The study group consists of 17 knees with trochlear dysplasia having undergone trochleoplasty for recurrent patellofemoral dislocation at a mean age of 22.4 years. The evaluation consisted in pre- and postoperative measurements on the proximal and distal trochlea on transverse CT scans in order to determine the morphological features. We measured the transverse position and depth of the trochlear groove, the transverse position of the patella, the ratio between the posterior patellar edge and the trochlear groove, the lateral patellar inclination angle, the sulcus angle, and the lateral trochlear slope. The trochlear groove lateralised a mean of 6.1 mm in the proximal aspect and 2.5 mm in the distal aspect of the trochlea, while the patella medialised a mean of 5 mm. Preoperatively the patella was lateral in relation to the trochlear groove in 13 cases, neutral in two cases, and medial in two cases. Postoperatively it was lateral in four cases, in neutral position in seven cases, and medialised in six cases, referenced to the trochlear groove. The trochlear depth increased from 0 to 5.9 mm postoperatively in the proximal aspect of the trochlea, and from 5.5 to 8.3 mm postoperatively in the distal trochlea. The lateral patellar inclination angle decreased from a mean of 21.9° to a mean of 7.8°. The sulcus angle decreased from a mean of 172.1° to a mean of 133° in the proximal trochlea and from a mean of 141.9° to a mean of 121.7° in the distal trochlea. The lateral trochlear slope changed from 2.8° to 22.7° in the proximal and from 14.9° to 26.9° in the distal part of the trochlea. In the CT scan patients with trochlear dysplasia demonstrated a poor depth, or even a flat or convex trochlea with a greater sulcus and lateral trochlear slope angle, a lateralised patella to the trochlear groove with poor congruency, and a greater lateral patellar inclination angle. Trochleoplasty can correct the pathological features of trochlear dysplasia by surgically creating more normal anatomy. The goal of this surgical procedure is to steepen and lateralise the trochlear groove for a better engagement of the patella.     

Patellar tendon length after anterior cruciate ligament reconstruction: a comparative magnetic resonance imaging study between patellar and hamstring tendon autografts

Patellar tendon shortening after anterior cruciate ligament reconstruction may be associated with anterior knee pain or patellofemoral arthritis. The present study was designed to compare postoperative changes in patellar tendon length after anterior cruciate ligament reconstruction between patellar tendon and hamstring tendon autograft. Magnetic resonance images of both knees (operated and healthy) and functional outcome were documented at least 1 year postoperatively in 16 patellar tendon harvested patients and in 32 hamstrings harvested patients. Patellar tendon length, patella length and Insall–Salvati ratio were measured. The operated knee values were compared to the respective values of the non-operated control knees. A significant 4.2 mm or 9.7% patellar tendon shortening in patellar tendon group and a non-significant 1.14 mm or 2.6% shortening in hamstrings group was detected. No significant difference was detected in terms of major shortening—patella baja—(6% for the patellar tendon group vs. 0% for the hamsting group). There was no significant difference in anterior knee problems between the two groups as evidenced by the Shelbourne score (94 for the patellar tendon group vs. 98 for the hamsting group). Harvesting of the patellar tendon for anterior cruciate ligament reconstruction resulted in a significant shortening of the remaining tendon. In contrast harvesting of the hamstring tendons did not affect significantly the patellar tendon length. However, the incidence of patella baja and overall functional outcome was not significantly different between the two groups. Paper presented at the 12th ESSKA 2000 Congress, Innsbruck, Austria, 2006 and also presented at the 5th Biennial ISAKOS Congress, Hollywood, FL, USA, 2005.     

Imaging patellar complications after knee arthroplasty

The purpose of this study is to describe complications affecting the patella in patients with total or partial knee arthroplasty. We respectively analysed plain-film radiographs, as well as ultrasound images when acquired, in a consecutive series of 1272 patients. The mean interval from knee replacement to patellar complications was 5 years and 7 months (range, 5 months to 14 years). The complications described include fracture, instability, dislocation or luxation, necrosis of the patella, infection of the patella, erosion of the patella, patellar impingement on the prosthesis and patellar or quadricipital tendon tear. We discuss the pathological imaging findings in the patella and their differential diagnosis after knee arthroplasty. Patellar complications after knee arthroplasty are uncommon but often potentially serious.     

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.