Abstract
Trochlear dysplasia is a risk factor for patellofemoral instability. Trochleoplasty involves reshaping the trochlear groove to provide increased patellofemoral stability. We obtained post-operative radiographs, MRI, and outcome scores in 6 patients who underwent this procedure. All 6 of the patients were satisfied with their outcome following trochleoplasty with no recurrent instability events. Mean bony sulcus angles decreased from 148 degrees to 129 degrees. However, 4 of the 6 patients reported anterior knee pain. Similar to previously published studies, trochleoplasty can reliably improve patellofemoral stability in patients with severe trochlear dysplasia, but a high percentage of patients will have pain postoperatively.
Introduction
Trochlear dysplasia is characterized by a shallow, flattened trochlear groove. A study done by Brattstroem in the 1960s observed an association between trochlear dysplasia and patellofemoral instability.1 This relationship has been studied to a much greater extent in Europe than it has in the United States. One form of treatment for patellofemoral instability in patients with severe trochlear dysplasia is a surgical procedure called trochleoplasty, in which the trochlear groove is reshaped to improve patellar stability. Although the efficacy of trochleoplasty has been shown to be high, many patients who have undergone this procedure have reported residual pain and degenerative joint disease postoperatively. This study seeks to evaluate the long term outcomes for patients who have undergone trochleoplasty.
Patellofemoral Anatomy and biomechanics
The patellofemoral joint consists of the articulation between the patella and the trochlea. The trochlea is a very complex osseus structure that varies in morphology from proximal to distal. Specifically, the lateral wall is highest proximally and decreases in height distally.1 In addition, there is extensive variability between individuals with regards to trochlear morphology.2 Bony and cartilage sulcus angles can be used to evaluate the anatomy of the trochlear groove. MRI has been advocated for visualization of the trochlea because chondral geometry allows for more accurate representation of trochlear anatomy.3,4,5 Stability of the patellofemoral joint is achieved by the coordinated action of static, dynamic, and osseus constraints.1,6 Static constraints include the medial retinacular structures, the MPFL and the medial patellotibial ligament, while the primary dynamic constraint is the vastus medialis obliquus muscle.
During full extension of the knee, the patella is proximal to the trochlear groove. In the first 20° to 30° of knee flexion, the MPFL guides the patella into the trochlear groove.7 When the knee has achieved 30° of flexion, the patella should be entirely constrained by the trochlear groove with less than 1 cm of lateral translation.8 At this point, the contribution of soft tissue constraints toward patellar stability becomes minimized, and the osseous constraint becomes the chief stabilizer of the joint.9 The height and angle of the trochlear groove provide the primary constraint against lateral patellar movement during continued knee flexion.10
Patellofemoral Instability
Several anatomic phenomena can contribute to patellofemoral instability. Deficient proximal medial restraints, trochlea dysplasia, patella alta, and malalignment (TT-TG > 20 mm) are risk factors for patellofemoral instability. A deficiency in the static or dynamic constraints can lead to improper centering of the patella into the trochlear groove during early knee flexion. In one study, Cash and Hughston demonstrated that there was a 43% risk for recurrent patellofemoral instability following non-surgical treatment of patellar instability in patients with predisposing factors, such as VMO dysplasia or trochlear dysplasia. However, in patients who were treated non-surgically for patellar instability who did not have predisposing factors to patellofemoral instability, this risk was reduced to 20%.11
Trochlear Dysplasia
Trochlear dysplasia has been shown to be present in < 2% of the population but in over 85% of people with recurrent patellofemoral instability.12 Dejour and Le Coultre found that 96% of patients with patellofemoral instability had trochlea dysplasia on plain x-rays.13
Dejour et al13 have developed a classification system that classifies trochlear dysplasia into four grades, differing in the severity of dysplasia. This classification system is dependent on the evaluation of lateral and axial radiographs (Figure 1).
Figure 1. Grades of trochlear dysplasia as described by dejour et al.
Type A trochlear dysplasia is characterized by a shallow groove when seen axially, the presence of a crossing sign on the lateral radiograph, and a bony sulcus angle of >145° (Figure 2). Type B trochlear dysplasia is characterized by the presence of a supratrochlear spur or prominence on the lateral radiograph as well as a flat trochlea when viewed axially. Type C trochlear dysplasia is characterized by a double contour when seen laterally and lateral convexity as well as medial hypoplasia when viewed axially (Figure 3). Type D trochlear dysplasia, the most severe grade, is characterized on lateral radiograph by a double contour and a supratrochlear spur, and it is seen axially as having asymmetric trochlear facets as well as a cliff between the medial and lateral facets.
Figure 2. CT image of severely dysplastic trochlea.
Figure 3. Lateral x-ray with crossing sign.
Figure 4. The sulcus deepening trochleoplasty as described by Dejour et al.
Figure 6. Post-trochleoplasty.
Treatment of Patellofemoral Instability
Each of the risk factors must be considered individually when selecting appropriate surgical management for these patients. In the patient that is skeletally mature with a normal TT-TG distance and absent patella alta, MPFL reconstruction is recommended even when trochlea dysplasia is present. A study performed by Steiner et al14 evaluated 34 patients with recurrent patellar instability and trochlear dysplasia who underwent MPFL reconstruction, and post-operatively there were no episodes of patellar instability or subluxation. When there is a TT-TG distance of >20 mm, the malalignment should be addressed with a tibial tubercle transfer.
The term trochleoplasty refers to any procedure in which the trochlea is reshaped to provide stability to the patellofemoral joint. Indications for trochleoplasty include recurrent patellofemoral instability with radiographic evident of severe trochlear dysplasia and failed previous patellofemoral surgical stabilization. Contraindications include patellofemoral joint degenerative disease and arthritis.15,16 Most descriptions of this procedure include either the open or arthroscopic removal of subchondral bone in the trochlea and subsequent compression of the cartilage into the newly deepened groove (Figures 3–8). Recurrent patellofemoral instability is very rare post-operatively, although residual pain is a common finding in studies following patients after trochleoplasty.21>,22
Figure 8. Undermining the cartilage and removing the subchondral bone.
Figures 5–8 are photos that were taken during a trochleoplasty.
Figure 5. Pre-trochleoplasty.
Figure 7. Demonstrating fixation.
Methods
IRB approval was obtained. Patients who had trochleoplasties performed in the past 10 years at the University of Iowa were located using CPT codes in the University of Iowa electronic medical record database. The patients were contacted and invited for followup. Lateral and Merchant x-ray views were obtained, from which bony sulcus angles and CD ratios were obtained. The presence of patella alta was also recorded. MRIs were obtained which were studied from the axial view to obtain TT-TG distance, cartilage sulcus angle, and the status of articular cartilage. Physical exams were performed, and data was collected, including: Q angle, apprehension test, moving patella apprehension test, presence of crepitus, patella tilt, lateral patella glide quadrant number, quadriceps strength, thigh circumference, Beighton score, and J sign. Outcome instruments used in this study include WOMAC and KOOS scores.
Table 1. Case 1 Physical exam data.
| Q angle | 15° |
| Apprehension | No |
| Crepitus | Significant grinding |
| Patella Tilt | Above |
| Quad strength | 5 |
| Hypermobility | Yes |
| J sign | No |
Table 2. Case 1 Radiographic and MRI data.
| Pre-operative crossing sign | Yes |
| Post-operative crossing sign | No |
| CD ratio | 1.48 |
| Pre-operative bony sulcus angle | 161° |
| Post-operative bony sulcus angle | 132° |
| Post-operative cartilage sulcus angle | 128° |
Case 1
15 year old female with history of recurrent patellar instability and chronic knee pain who underwent a trochleoplasty after recurrent patellofemoral instability status post tibia tubercle transfer. After tibial tubercle transfer, she still had recurrent patellar instability.
Description of procedure
The surgical approach was through the previous anterior and longitudinal incision. The extensor mechanism was exposed. Given her previous lateral release and medial imbrication, a lateral parapatellar arthrotomy was performed extending from the vastus lateralis down to the lateral aspect of the tibial tubercle. Two screws were then removed from the tibial tubercle without difficulty from her previous osteotomy of the tubercle. A lateral parapatellar arthrotomy was then completed. The patella was everted. The patellar articular surface appeared to be maintained. There was significant dysplasia and hypoplasia of her trochlea. A burr was used to remove the bone beneath the articular cartilage of the (subchondral excavation) trochlea, leaving the full thickness cartilage and a thin layer of bone intact. Once it was possible to ballot the cartilage surface over the excavation, the cartilage down the middle of the trochlea was incised with a 10 blade or a very sharp osteotome and the cartilage could be compressed, both medially and laterally, creating a deep groove. The cartilage was then fixed and placed using four suture anchors with #2 suture and suture bridge construct. After the trochleoplasty was complete, a MPFL reconstruction was performed with allograft.
Figure 9. Case 1 Pre-operative Merchant x-ray.
Figure 10. Case 1 Post-operative Merchant x-ray.
The patient's bony sulcus angle decreased from 142° to 109°, and the MRI demonstrated a cartilage sulcus angle of 114°. These sulcus angles demonstrate that Patient 1 had a deeper trochlear groove post-operatively which should provide resistance against lateral patella movement and patellar dislocations. In fact, this patient reported no cases of patellofemoral instability after her trochleoplasty. Her pre-operative WOMAC score was 66.5% while her post-operative WOMAC score improved to 27.1%. Post-operatively, her KOOS survey showed a score of 63%. The patient stated that she was satisfied with this procedure.
Table 3. Case 2 Physical exam data.
| Q angle | 10° |
| Apprehension | No |
| Crepitus | Significant grinding |
| Patella Tilt | Neutral |
| Quad strength | 5.0 |
| Hypermobility | Yes |
| J sign | No |
Table 4. Case 2 Radiographic and MRI data.
| Pre-operative crossing sign | Yes |
| Post-operative crossing sign | No |
| CD ratio | 1.48 |
| Pre-operative bony sulcus angle | 161° |
| Post-operative bony sulcus angle | 132° |
| Post-operative cartilage sulcus angle | 128° |
Case 2
17 year old female with history of recurrent patellar instability and chronic knee pain. Previous surgery had included a distal realignment and medial imbrication which failed to provide patellar stability.
Description of procedure
The patient's previous anterior longitudinal incision was used. A lateral parapatellar arthrotomy was made next to the patella. This served also as a lateral release. Two 3.5 fully threaded screws were removed from the tibial tubercle at the patient's request.
The patient had a very dysplastic medial and lateral femoral condyle with virtually no groove. The same technique described in case #1 was used to create the trochleoplasty. This deepened the sulcus approximately 1 cm. A MPFL reconstruction was performed after completion of the trochleoplasty.
The patient in case 2 originally had a bony sulcus angle of 161°, which was reduced to 132° post-operatively. This signifies a deeper trochlear groove, thus providing joint stability. Her axial MRI displayed a cartilage sulcus angle post-operatively of 128°. Patient 2 had a pre-operative WOMAC score of 80%, indicating that she was dissatisfied with the state of her knee. Post-operatively, this was greatly improved to 22%, and in addition, her post-operative KOOS score was 65%. At follow-up, the patient reported mild pain but no instability whatsoever. She also stated that she was satisfied with her trochleoplasty procedure.
Figure 11. Case 2 Pre-operative Merchant x-ray.
Figure 12. Case 2 Post-operative Merchant x-ray.
Table 5. Case 3 Physical exam data.
| Q angle | 18° |
| Apprehension | No |
| Crepitus | Mild grinding |
| Patella tilt | Above |
| Quad strength | 5 |
| Hypermobility | No |
| J sign | No |
Table 6.
Case 3 Radiographic and MRI data
| Pre-operative crossing sign | N/A |
| Post-operative crossing sign | Yes |
| CD ratio | 1.26 |
| Pre-operative bony sulcus angle | N/A |
| Post-operative bony sulcus angle | 127° |
| Post-operative cartilage sulcus angle | 119° |
Case 3
16 year old female with a history of recurrent patellar instability. She reported an average of 2–3 patellar dislocations per week. Prior to her trochleoplasty, two other surgeries had been attempted, including an arthroscopic lateral release and an open VMO advancement.
Description of procedure
A midline incision was made over the patella and carried proximally for a distance of approximately 4.5 cm distally. A medial arthrotomy was done because of the previous approach. The trochlear groove was noted to be very small and shallow. The patella itself had minimal cartilage wear but was very small and easily mobile. Trochleoplasty was performed as described previously. Following the trochleoplasty, a tibial tubercle transfer was performed.
The patient in case 3 had a post-operative bony sulcus angle of 127°, and her post-operative cartilage sulcus angle was 119°. Although her pre-operative outcome scores were not available, her post-operative WOMAC score was 0%, and her post-operative KOOS score was 98.2%. These two scores indicate that patient 3 was extremely satisfied with the status of her knee. At the time of follow-up, she reported no pain and no episodes of patellofemoral instability. The patient stated she was fully satisfied with her operation.
Figure 13. Case 3 Post-operative Merchant x-ray.
Figure 14. Case 3 Post-operative axial MRI.
Table 7. Case 4 Physical exam data.
| Q angle | 12° |
| Apprehension | No |
| Crepitus | Mild grinding |
| Patella Tilt | Above |
| Quad strength | 5 |
| Hypermobility | No |
| J sign | Yes |
Table 8. Case 4 Radiographic and MRI data.
| Pre-operative crossing sign | N/A |
| Post-operative crossing sign | Yes |
| CD ratio | 1.36 |
| Pre-operative bony sulcus angle | N/A |
| Post-operative bony sulcus angle | 135° |
| Post-operative cartilage sulcus angle | 130° |
Case 4
17 year old female with a history of recurrent patellar instability, reporting 2–3 episodes of patellofemoral instability per week. Prior to her trochleoplasty, an arthroscopic lateral release had been performed, but she stated that this procedure afforded her little to no relief.
Description of procedure
A longitudinal incision in line with the previous incision was made excising the previous scar. A medial arthrotomy was then made. The patella was everted and the trochlea was inspected. It was found to be significantly hypoplastic with virtually no groove present. Trochleoplasty was performed in the usual fashion. After the trochleoplasty was completed, a tibia tubercle transfer and medial imbrication were performed.
Patient 4 had a post-operative bony sulcus angle of 135° and a cartilage sulcus angle of 130°. Once again, because the procedure was performed several years ago, pre-operative imaging and outcome scores were unavailable. The patient's post-operative WOMAC score was 0%, and her KOOS score was 98.2%, signifying great satisfaction with the procedure. She reported that she had no post-operative pain or instability, and she was thoroughly satisfied with the procedure.
Figure 15. Case 4 Post-operative Merchant x-ray.
Figure 16. Case 4 Post-operative Axial MRI.
Table 9. Case 5 Physical exam data.
| Q angle | 20° |
| Apprehension | No |
| Crepitus | Improved post-operatively |
| Patella Tilt | Above |
| Quad strength | 5 |
| Hypermobility | No |
| J sign | No |
Table 10. Case 5 Radiographic and MRI data.
| Pre-operative crossing sign | Yes |
| Post-operative crossing sign | No |
| CD ratio | 1.16 |
| Pre-operative bony sulcus angle | 143° |
| Post-operative bony sulcus angle | 124° |
| Post-operative cartilage sulcus angle | 138° |
Case 5
38 year old female with a history of recurrent patellar instability and knee pain. She is an amateur bodybuilder, and thus her patellofemoral instability severely limited her normal level of activity. Prior to her trochleoplasty, a Fulkerson osteotomy was performed, which provided her little relief from patellar instability.
Description of procedure
A midline incision was made. Following the medial arthrotomy, the patella was then retracted laterally . A #1 Vicryl was used to create double row suture fixation with overlap of the VMO and the medial retinacular structures. Approximately, 30–40% overlapped over the patella. The double row fixation was completed. Trochleoplasty was performed as previously described.
Patient 5 had a pre-operative bony sulcus angle of 143°, and this was reduced to 124° post-operatively. The post-operative cartilage sulcus angle was 138°. The patient's pre-operative WOMAC score was 66%, which improved to 8% at the time of follow-up. Her KOOS score at this time was 82%. Her follow-up outcome scores indicate that she was satisfied with the procedure. The patient reported that post-operatively, she had mild, residual pain but no episodes of patellofemoral instability She also stated that she was entirely satisfied with the procedure.
Figure 17. Case 5 Pre-operative Merchant x-ray.
Figure 18. Case 5 Post-operative Merchant x-ray.
Table 11. Case 6 Physical exam data.
| Q angle | 10° |
| Apprehension | No |
| Crepitus | Minimal |
| Patella Tilt | Neutral |
| Quad strength | 4 |
| Hypermobility | No |
| J sign | Yes |
Table 12. Case 6 Radiographic and MRI data.
| Pre-operative crossing sign | No |
| Post-operative crossing sign | No |
| CD ratio | 1 |
| Pre-operative bony sulcus angle | 150° |
| Post-operative bony sulcus angle | 123° |
| Post-operative cartilage sulcus angle | 120° |
Case 6
26 year old male with a history of recurrent patellar instability and chronic, debilitating knee pain. The patient's trochleoplasty was his first knee operation. Although in most cases, previous surgery has failed to stabilize the patellofemoral joint, it was very clear in this case that the trochlea was severely dysplastic.
Description of procedure
The knee was taken through a range of motion and it was found the patella was noted to spontaneously dislocate at 30 degrees of flexion. A longitudinal anterior incision was taken from the superomedial aspect of the patella to the lateral aspect of the tibial tubercle. Attention was first turned to the tibial tubercle medialization. This was fixed with two screws.
A medial parapatellar incision was then created sharply, using a knife and the patella was dislocated laterally. The trochlea was quite shallow and was dysplastic. There was evidence of grade II to grade III chondromalacia of the lateral femoral condyle and of the central inferior patella, especially on the lateral side. A small bur was then used to excavate the bone underneath the central portion of the trochlea. Small curettes were used to create a V-shaped deepening beneath the trochlea. A 15 blade was then used to incise the cartilage of the trochlea, which was then pressed down, creating a deeper groove for the trochlea. A total of six 0 Vicryl sutures were placed in inverted mattress fashion along the cartilage edge in the trochlear groove, which were then tapped down into the trochlea using 3.5-mm Bio-PushLock anchors and holding the cartilage down into the newly deepened trochlear groove. Bone graft from the excavation and from the proximal tibia was then placed along the area of the excavation, filling in any defects. Last, an MPFL reconstruction was performed.
Figure 19. Case 6 Pre-operative Merchant x-ray.
Figure 20. Case 6 Post-operative Merchant x-ray.
Patient 6 had a pre-operative bony sulcus angle of 150° and a post-operative angle of 123°. The postoperative cartilage sulcus angle was 120°. The patient's pre-operative and post-operative WOMAC scores were 67% and 65%, and his post-operative KOOS score was 41%. However, the patient stated that he was somewhat satisfied with the procedure because he had not had any episodes of instability after his trochleoplasty.
Summary of Results
A total of 12 trochleoplasties had been performed in the past 10 years at the University of Iowa. Six of these knees were able to be evaluated in this study. The averages of many of the parameters in this study are summarized in Table 13.
Table 13. Average data for all patients.
| Parameter | Mean |
|---|---|
| Age at surgery | 21.5 years |
| Time since surgery at follow-up | 68.3 months |
| Thigh circumference | 43.2 cm |
| Quadriceps strength | 4.8 |
| Pre-operative bony sulcus angle | 149° |
| Post-operative bony sulcus angle | 126.2° |
| CD ratio | 1.3 |
| Cartilage sulcus angle | 125° |
| Post-operative WOMAC score | 20% |
| Post-operative KOOS score | 74.50% |
Discussion
Stability of the patellofemoral joint is achieved by the coordinated action of static, dynamic, and osseous constraints. Beyond 20° to 30° of knee flexion, osseous constraints become the predominant form of resistance against patellar subluxation. Trochlear dysplasia is characterized by a shallow trochlear groove with reduced resistance to lateral patellar movement. It is strongly associated with patellofemoral instability. Because of the myriad etiologies of patellofemoral instability, there are various options for surgical intervention, including extensor mechanism realignment, soft tissue balancing and ligament reconstruction. Trochleoplasty is a procedure defined as the surgical reshaping of the trochlear groove to provide resistance against lateral patellar translation, and it is uncommonly utilized. Although residual pain is often present, trochleoplasty is very effective at providing patellofemoral stability.17, 18, 19, 20, 21
Several studies have been performed evaluating the long-term outcomes of trochleoplasty; however, these are primarily European studies, as trochleoplasty has not been widely studied in the United States. The results from the studies are summarized in Table 14.
Table 14. Data from other studies evaluating trochleoplasty outcomes.
| Investigator | # of Knees | Average follow-up time (months) | Recurring PF Instability | Residual pain | Outcome |
|---|---|---|---|---|---|
| Koch et al | 2 | 6 | 0% | 0% | Subjective – very good |
| Verdonk et al | 13 | 18 | 0% | N/A | 77% satisfied |
| Donell et al | 17 | 36 | 0% | N/A | 82% satisfied |
| Schöttle et al | 19 | 36 | 0% | 26% | Kujala score – 56 to 80 |
| Utting et al | 59 | 24 | 0% | 29.60% | 92% satisfied, IKDC 54 to 72 |
| Fucentes et al | 44 | 48 | 2.20% | N/A | 76% satisfied |
| This study | 6 | 68 | 0% | 66% | 100% satisfied |
Our findings are similar to European outcomes following trochleoplasty.17, 18, 19, 20, 21, 22 The six knees evaluated at the University of Iowa were seen at an average follow-up time of 68 months, and the average bony sulcus angle decreased from 149° to 128°, indicating deepening of the trochlear groove. In this study, success rate was defined as both subjective patient satisfaction as well as the absence of post-operative patellofemoral instability. All of the patients in this study reported satisfaction with their procedure. Although one patient reported severe post-operative pain, he was happy with the patellofemoral stability. None of the patients in this study reported postoperative instability; however, 4/6 (66%) of the patients reported at least some residual pain. Although there was a high proportion of patients with residual anterior knee pain, this must be viewed closely at an individual basis. Two of the patients (three knees) reported having sustained trauma to the knee within one week prior to their follow-up, and this may have affected the presence of pain at the time of their clinical visit. One of these patients was also an amateur bodybuilder, and thus her heavy squatting may also have been one etiology for her pain.
In this study, 5 of the 6 patients had numerous previous surgeries prior to the trochleoplasty and continued to have patellar instability. With a dysplastic trochlea, the patella is not stable despite corrections in alignment and soft tissue stabilization. In severe trochlear dysplasia, there is convexity near the proximal edge of the trochlea. In these cases, soft tissue stabilization and a tubercle transfer are not enough to prevent recurrent patellofemoral instability.
Because of the rarity of this procedure, the sample size in this study was small (n=6), which reduced the statistical power of this study. A total of 10 patients (12 trochleoplasties) have been performed in the last 10 years at the University of Iowa. Although 6/12 of the knees were available to evaluation, 6 of the patients did not return for follow-up. Two of the patients were not able to reached, one patient died, and 2 others did not want to come back.
This is the first study performed in the United States evaluating long term outcomes following trochleoplasty. Based on this study, trochleoplasty should be viewed as a necessary procedure in cases of severe trochlea dysplasia when patellofemoral stability cannot be obtained by proximal or distal reconstruction. Although patients often report the presence of post-operative residual pain, there is a very high success rate in preventing future episodes of patellofemoral instability as well as a high subjective patient satisfaction rate.
References
- 1.Brattstroem H. Shape of the intercondylar groove normally and in recurrent dislocation of the patella: A clinical and x-ray anatomical investigation. Acta Orthop Scand Suppl. 1964;68:1–148. (suppl) [PubMed] [Google Scholar]
- 2.Feller JA, Amis AA, Andrish JT, Arendt EA, Erasmus PJ, Powers CM. Surgical biomechanics of the patellofemoral joint. Arthroscopy. 2007;23(5):542–553. doi: 10.1016/j.arthro.2007.03.006. [DOI] [PubMed] [Google Scholar]
- 3.van Huyssteen AL, Hendrix MR, Barnett AJ, Wakeley CJ, Eldridge JD. Cartilage bone mismatch in the dysplastic trochlea: An MRI study. J Bone Joint Surg Br. 2006;88(5):688–691. doi: 10.1302/0301-620X.88B5.16866. [DOI] [PubMed] [Google Scholar]
- 4.Shih YF, Bull AM, Amis AA. The cartilaginous and osseous geometry of the femoral trochlear groove. Knee Surg Sports Traumatol Arthrosc. 2004;12(4):300–306. doi: 10.1007/s00167-003-0414-3. [DOI] [PubMed] [Google Scholar]
- 5.Salzmann GM, Weber TS, Spang JT, Imhoff AB, Schöttle PB. Comparison of native axial radiographs with axial MR imaging for determination of the trochlear morphology in patients with trochlear dysplasia. Arch Orthop Trauma Surg. 2010;130(3):335–340. doi: 10.1007/s00402-009-0912-y. [DOI] [PubMed] [Google Scholar]
- 6.Fithian DC, Nomura E, Arendt E. Anatomy of patellar dislocation. Operative Techniques in Sports Medicine. 2001;9:102–111. [Google Scholar]
- 7.Desio SM, Burks RT, Bachus KN. Soft tissue restraints to lateral patellar translation in the human knee. Am J Sports Med. 1998;26(1):59–65. doi: 10.1177/03635465980260012701. [DOI] [PubMed] [Google Scholar]
- 8.Ahmad CS, McCarthy M, Gomez JA, Shubin Stein BE. The moving patellar apprehension test for lateral patellar instability. Am J Sports Med. 2009;37(4):791–796. doi: 10.1177/0363546508328113. [DOI] [PubMed] [Google Scholar]
- 9.Lee TQ, Yang BY, Sandusky MD, McMahon PJ. The effects of tibial rotation on the patellofemoral joint: Assessment of the changes in in situ strain in the peripatellar retinaculum and the patellofemoral contact pressures and areas. J Rehabil Res Dev. 2001;38(5):463–469. [PubMed] [Google Scholar]
- 10.Jafaril A, Farahmand F, Meghdari A. The effects of trochlear groove geometry on patellofemoral joint stability: A computer model study. Proc Inst Mech Eng H. 2008;222(1):75–88. doi: 10.1243/09544119JEIM255. [DOI] [PubMed] [Google Scholar]
- 11.Cash JD, Hughston JC. Treatment of acute patellar dislocation. Am J Sports Med. 1988;16(3):244–249. doi: 10.1177/036354658801600308. [DOI] [PubMed] [Google Scholar]
- 12.Dejour H, Walch G, Nove-Josserand L, Guier C. Factors of patellar instability: an anatomic radiographic study. Knee Surg Sports Traumatol Arthrosc. 1994;2(1):19–26. doi: 10.1007/BF01552649. [DOI] [PubMed] [Google Scholar]
- 13.Dejour D, Le Coultre B. Osteotomies in patello-femoral instabilities. Sports Med Arthrosc. 2007;15(1):39–46. doi: 10.1097/JSA.0b013e31803035ae. [DOI] [PubMed] [Google Scholar]
- 14.Steiner TM, Torga-Spak R, Teitge RA. Medial patellofemoral ligament reconstruction in patients with lateral patellar instability and trochlear dysplasia. Am J Sports Med. 2006;34(8):1254–1261. doi: 10.1177/0363546505285584. [DOI] [PubMed] [Google Scholar]
- 15.Schöttle PB, Fucentese SF, Pfirrmann C, Bereiter H, Romero J. Trochleaplasty for patellar instability due to trochlear dysplasia: A minimum 2-year clinical and radiological follow-up of 19 knees. Acta Orthop. 2005;76(5):693–698. doi: 10.1080/17453670510041781. [DOI] [PubMed] [Google Scholar]
- 16.Dejour D, Saggin P. The sulcus deepening trochleoplasty: The Lyon's procedure. Int Orthop. 2010;34(2):311–316. doi: 10.1007/s00264-009-0933-8. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 17.Koch PP, Fuchs B, Meyer DC, Fucentese SF. Closing wedge patellar osteotomy in combination with trochleoplasty. Acta Orthop Belg. 2011;77(1):116–21. Feb. [PubMed] [Google Scholar]
- 18.Verdonk R, Jansegers E, Stuyts B. Trochleoplasty in dysplastic knee trochlea. Knee Surg Sports Traumatol Arthrosc. 2005;13(7):529–33. doi: 10.1007/s00167-004-0570-0. Oct. Epub. 2005 Jan 11. [DOI] [PubMed] [Google Scholar]
- 19.Donell ST, Joseph G, Hing CB, Marshall TJ. Modified Dejour trochleoplasty for severe dysplasia: operative technique and early clinical results. Knee. 2006;13(4):266–73. doi: 10.1016/j.knee.2006.01.004. Aug. Epub 2006 Apr 24. [DOI] [PubMed] [Google Scholar]
- 20.Schöttle PB, Fucentese SF, Pfirrmann C, Bereiter H, Romero J. Trochleaplasty for patellar instability due to trochlear dysplasia: A minimum 2-year clinical and radiological follow-up of 19 knees. Acta Orthop. 2005;76(5):693–698. doi: 10.1080/17453670510041781. [DOI] [PubMed] [Google Scholar]
- 21.Utting MR, Mulford JS, Eldridge JD. A prospective evaluation of trochleoplasty for the treatment of patellofemoral dislocation and instability. J Bone Joint Surg Br. 2008;90(2):180–5. doi: 10.1302/0301-620X.90B2.20017. Feb. [DOI] [PubMed] [Google Scholar]
- 22.Fucentese Sandro F., Zingg Patrick O., Jürgen Schmitt, Pfirrmann Christian W. A., Meyer Dominik C., Koch Peter P. Classification of trochlear dysplasia as predictor of clinical outcome after trochleoplasty. Knee Surg Sports Traumatol Arthrosc. 2011;19(10):1655–61. doi: 10.1007/s00167-011-1410-7. Oct. Epub 2011 Feb 8. [DOI] [PubMed] [Google Scholar]