Introduction

 

By nature, the patellofemoral joint has low congruity. Passive stability is provided both by the bony structures (congruity between the patella and the trochlear groove) and by the medial and lateral ligaments. Active stability depends on correct tension of the quadriceps muscles on the one hand, and on passive medial-lateral soft-tissue balance on the other hand. The patella needs both passive and active stability to transmit the quadriceps muscle force during flexion and extension movements, whether it be during normal gait cycle or high energy sports activities.

 

In 1987, Henri Dejour's team developed a classification of patellofemoral disorders including three categories : 1) patellar pain syndrome, 2) potential instability (lateral tracking patella), 3) objective patellar instability.6 It did not take into account a possible history of patellar dislocation or the possible presence of at least one of the four main factors of instability. An algorythm (so-called "Menu à la carte") was developed for surgical management of objective instabilities. Its aim was to address each anatomic abnormality individually.

As a matter of fact, objective patellar instability treated according to this protocol had a low recurrence rate.18,19 However, in 10-15% of the cases, procedures like medialization, distal transfer of the tibial tubercle and/or plasty of the vastus medialis were associated with postoperative pain, occasionally patellar maltracking, and in 1 to 5% of the cases with recurrent dislocation.17,19 It was found that these patients had severe trochlear dysplasia. This condition results in abnormal kinematics with patellar tilt in the horizontal plane, and in impingement of the patella upon prominence of the trochlea in flexion and extension in the sagittal plane (Fig. 1). Both anomalies may cause cartilage lesions involving 100% of the central portion of the patella. Therefore, they are potentially most important factors in promoting later development of patellofemoral osteoarthritis3 (78% of patients with patellofemoral osteoarthritis have a trochlear dysplasia).

 

Main factors of patellar instability (1987) Trochlear dysplasia Patella Alta Excessive TT-TG distance Patellar tilt     96% True dislocation   3% Control Index > 1.2   30% True dislocation   0% Control > 20 mm   56% True dislocation   12 mm Control > 20°   83% True dislocation   "Menu à la carte" - H. Dejour, 1987 Trochleoplasty ? Distal transfer of the tibial tubercle Medialization of the tibial tubercle Plasty of the vastus medialis - Insall technique

 

Indications

 

In 1987, H. Dejour and G. Walch proposed a classification of trochlear dysplasia including 3 types.22 Trochlear dysplasia was defined by a positive crossing sign (sulcus line crossing the anterior aspect of the femoral condyles). The 3 types corresponded to the levels at which crossing occurred. The Lille's team showed the difficulty to reach a consensus (lack of interobserver agreement) about identification of the different types, particularly Type III.4 In 1998, D. Dejour and B. Lecoultre studied a group of patients with objective patellar instability and analysed 177 lateral radiographs and CT scans. This led them to refine the initial classification by adding two new signs, the supratrochlear spur (prominence of the trochlea), and the double contour (projection on the lateral view of the hypoplastic medial trochlear facet) (Fig. 2). By overlaying chondral bone density patterns of the medial and lateral facets onto the sulcus line in the sagittal analysis (Fig. 3), a correspondence can be established between the horizontal plane (CT evaluation) and the sagittal plane (radiographic evaluation), which provides a better understanding of the crossing sign and double contour. Based on this, 4 types of trochlear dysplasia4,20,21 (Fig. 4) can be distinguished. According to F. Remy and F. Gougeon, this new classification ensures high consistency in interobserver grading (coeff. = 0.65).

 

Deepening trochleoplasty is indicated in patients with recurrent dislocation of the patella (RDP), and severe radiographic trochlear dysplasia with dome-shaped trochlea. Types B and D are the best indications. It is less suitable for treatment of Type C.8,16

Deepening trochleoplasty is almost always associated with procedures which address all other factors of instability including patellar height, tibial tubercle-trochlear groove (TT-TG) distance,10 and patellar tilt. If patellar index is greater than 1.2, distal transfer of the tibial tubercle is performed. If it exceeds 20 mm, distal realignment through medialization of the tibial tubercle may be considered ; however, it must be pointed out that correction of the trochlear anomaly will affect the position of the trochlear groove, resulting in proximal realignment. This is why medialization is not always needed. Patellar tilt can be partly corrected by reshaping of the trochlear groove (there is a high statistical correlation between the shape of the trochlear groove and the amount of patellar tilt). In the algorythm developed in 1987, reshaping of the trochlear groove was usually associated with plasty of the vastus medialis (Insall technique).13 Attempts to correct patellar tilt using the Insall technique alone yielded poor results, with an average correction of 6° with the quadriceps contracted and 4.5° with the quadriceps relaxed. Since 2005, plasty of the vastus medialis has been given up in favor of repair of the medial patellofemoral ligament.9 Results are currently under evaluation.

 

Fig. 1: Abnormal patellar kinematics due to trochlear dysplasia in both the horizontal and sagittal planes, with excessive patellar tilt and impingement of the mid-portion of the patella upon prominence of the trochlea.

Fig. 2: Presence of the three signs of trochlear dysplasia: crossing sign, supratrochlear spur, and double contour on a lateral radiograph.

Fig. 3: Sulcus lines displayed in both the horizontal and sagittal planes. a/ Normal trochlea: tip of lateral facet > sulcus line < tip of medial facet b/ Flat trochlea (crossing sign): tip of lateral facet = sulcus line = tip of medial facet c/ Lateral convexity (double contour): tip of lateral facet = sulcus line > tip of medial facet

Fig. 4: Classification of trochlear dysplasia (D. Dejour) Type A: Crossing sign and shallow trochlea Type B: Crossing sign, supratrochlear spur, flat trochlea Type C: Crossing sign, double contour, trochlear facet asymmetry Type D: Types B + C, trochlear facet asymmetry, cliff pattern

SURGICAL TECHNIQUE

 

This technique was first described by Masse in 1978 (RCO)11. Later on in 1987, it was modified and standardized by Henri Dejour.8 The primary goal of this procedure was to deepen the trochlear depth and restore a sulcus angle of approximately 145°. It is technically more demanding than open-wedge procedures such as the Albee procedure whereby the lateral femoral condyle is elevated by inserting a wedge of bone graft, but it is much more etiological. As a matter of fact, by addressing the trochlear dysplasia parameters, that is, prominence of the trochlea and insufficient trochlear depth, the root cause of dislocation of the extensor mechanism is eliminated.

 

The procedure is performed using an anteromedial approach, whether a MIS midvastus approach or a traditional anteromedial approach, if a tibial tubercle transfer is necessary. The patella and the trochlear groove are exposed, and cartilage lesions are assessed using the ICRS system. In no case the patella is everted.

A marking pen is used to define the new trochlear groove and outline the medial and lateral facets (Fig. 5). The new trochlear groove should be oriented 3-6° laterally from distal to proximal. The anatomic landmark for the inferior limit of the trochlear groove is the point where the two condyles meet. The superior limit is dictated by the patient's anatomy.

The proximal part of the trochlea is exposed and periosteal stripping is performed around the edge of the trochlea. Cortical bone is removed from around the trochlea using a narrow osteotome and the underlying cancellous bone is exposed. A power burr equipped with an adjustable stylus is used to determine the appropriate resection depth, avoid penetration of the cartilage, or cause damage to the cartilage due to heat generation. A minimum residual thickness of about 4 mm consisting of cartilage and a thin layer of chondral bone is recommended to achieve a bone surface that will be easy to fashion (Fig. 6). The remaining cancellous bone is removed using a small curette. The cancellous bone bed should extend as far as to the roof of the femoral notch. Once proper trochlear depth has been achieved, attention is directed to the preparation of the medial and lateral facets.

In most cases, an osteoclasis is performed in the middle of the trochlear groove using a scalpel to allow bone shell impaction into the new sulcus. The new facets are then fixed with two metal staples fashioned from 1 mm diameter Kirschner wires (Fig. 7). The margins of the trochlea are grafted using cancellous bone obtained during preparation. Patellar tracking is checked again.

ICRS grade 3 cartilage lesions may impose resection of cartilage flaps, or cartilage scales in chondritis with cartilage exfoliation. In the presence of severe patellar cartilage damage with grade 4 lesions which expose the subchondral bone, one may have to create microfractures or to discuss the surgical options.

 

Fig. 5: Outlining the new trochlear groove and facets

Fig. 6: Underlying cancellous bone is removed using a power burr equipped with an adjustable stylus

Fig. 7: Bone shell impaction into the new sulcus and fixation with two 1 mm diameter metal staples

Fig. 8: Deepening trochleoplasty associated with repair of the medial patellofemoral ligament

Fig. 9:
a/ Postoperative lateral view: no prominence of the trochlea
b/ Merchant view
c/ Scan image shows perfect correction of patellar tilt and normal trochlear groove. Note the MPFL repair
d/ Same control CT scan

9a 9b 9c 9d

POSTOPERATIVE CARE

 

After a trochleoplasty, immediate weight-bearing is allowed with no restriction of movement. During the first postoperative days, the use of a CPM (continuous passive motion) machine is recommended to allow the knee joint to slowly move in flexion and extension. Thus, the trochlear groove will be gently and gradually fashioned. Furthermore, continuous knee motion stimulates articular cartilage nutrition.

 

Trochleoplasty is very often associated with other procedures such as distal transfer of the tibial tubercle12, medialization of the tibial tubercle, or a medial procedure like repair of the medial patellofemoral ligament. All associated procedures should be taken into account when establishing the rehabilitation protocol.

Since 2005, this deepening trochleoplasty technique has been systematically associated with reconstruction of the medial patellofemoral ligament using the gracilis tendon. Two parallel bone tunnels are drilled in the medial border of the patella. The tendon graft is advanced into the first tunnel and pulled back through the second one, forming a loop inside the patella. Then, the transplant is passed through the deep subcutaneous tissue down to and slightly posterior to the tip of the medial epicondyle, which is the most isometric position (Fig. 8). Lastly, it is fixed in a blind tunnel using an interference screw. We personally do not perform plasty of the vastus medialis as effectiveness of this procedure in correcting patellar tilt is not conclusive.

Results of the first cases were presented during the "Journées Lyonnaises de Chirurgie du Genou" in 2002 (Fig. 9 a,b,c,d). The patient population was divided into two groups : group I included only patients with a history of prior kneecap surgery, who therefore had recurrent instability or pain. Group II included patients with primary patellar dislocation.5

 

Group I

 

Group I included 18 patients in whom patellofemoral surgery had failed. Mean age was 24 years, mean follow-up was 6 years (range, 2-8 years). No patient had been lost to follow-up. Indications for trochleoplasty were pain ⁽⁶⁾ and recurrent instability ⁽¹²⁾. On average, patients had had 2 previous surgeries (i.e. medialization, arthroscopy, distal transfer, sectioning of the medial retinaculum etc ...).

 

Preoperatively, there were 8 Type B trochlear dysplasias, 4 Type C, and 6 Type D. Mean TT-TG distance was 18 mm (range, 14-24 mm), Caton & Deschamps index was 1.1 mm (range, 0.8-1.3 mm), and mean patellar tilt was 35° (range, 18-48°).

Deepening trochleoplasty was associated with medialization of the tibial tubercle in 8 knees, and with distal transfer of the tibial tubercle in 6. All patients had plasty of the vastus medialis.

Patients were reviewed for clinical and radiological evaluation using the IKDC score : 65% of the patients were satisfied or very satisfied; knee stability was graded A in 13 patients, B in 5; 28% of the patients had residual pain which was correlated with the condition of the patellofemoral cartilage. Two patients developed patellofemoral osteoarthritis. There was no recurrence of instability.

As regards radiological evaluation, mean patella index was 1 (range, 0.8-1.1), mean TT-TG distance was 12 mm (range, 6-17 mm), mean patellar tilt with quadriceps relaxed was 21° (range, 11-28°) and with quadriceps contracted 24° (range, 16-30°).

 

Group II

 

Group II included 44 patients with no prior surgery. Mean age at operation was 23 years, mean follow-up was 7 years (range, 2-9 years). Two patients had been lost to follow-up. Trochleoplasty was associated with medialization in 22 knees, distal transfer of the tibial tubercle in 26, and plasty of the vastus medialis in 32.

 

Preoperatively, there were 21 Type B trochlear dysplasias, 12 Type C, and 11 Type D. Mean TT-TG distance was 24 mm (range, 15-32 mm), Caton & Deschamps index was 1.3 mm (range, 1.0-1.4 mm), and mean patellar tilt was 33° (range, 24-57°).

Deepening trochleoplasty was associated with medialization of the tibial tubercle in 8 knees, and with distal transfer of the tibial tubercle in 6. All patients had plasty of the vastus medialis.

Patients were reviewed for clinical and radiological evaluation using the IKDC score : 85% of the patients were satisfied or very satisfied; knee stability was graded A in 31 cases, B in 13; 5% of the patients had residual pain uncorrelated with the intraoperative condition of the patellofemoral cartilage.

No patient developed patellofemoral osteoarthritis. There was no recurrence of instability.

As regards radiological evaluation, mean patella index was 1 (range, 1.0-1.1), mean TT-TG distance was 16 mm (range, 14-21 mm), mean patellar tilt with quadriceps relaxed was 18° (range, 9-30°) and with quadriceps contracted 22° (range, 14-34°).

Analysis of these two small series shows that patients in Group I have a very high risk of developing osteoarthritis and still suffer relatively severe pain. This study demonstrates that in revision cases, trochleoplasty is indeed associated with potential hazards and may increase the risk of developing osteoarthritis. Therefore, only recurrent patellar instability can justify reoperation, not persistent pain.

In contrast, deepening trochleoplasty is an excellent option for Group II patients. As a matter of fact, experience shows that in these patients, better correction of patellar tilt is achieved when trochleoplasty is performed. Furthermore, the rate of residual pain is only 5% in this high-risk population with severe preexisting abnormalities.

 

Typical prescription for CT scan of the patella   CT scan Protocol - Lyon Patellar Instability   1 - Scanning protocol       Patient positioning: patient is supine with the knee joints in extension and the feet together (tape the feet together, if necessary).       AP topogram: -  1st acquisition: quadriceps relaxed .  bone filter (UHR: ultra-high resolution) .  Multislice helical CT; scan area: from the apex of the patella to the tibial tubercle; 1 mm slices, overlapping slices every 0.6 mm; pitch = 1   -  2nd acquisition : quadriceps contracted .  bone filter (UHR) .  4 slices with a thickness of 3 or 5 mm; highest slice in mid-portion of the patella (centering: manual or from topogram image).   2 - Data analysis   Provide about 20 transverse multiplanar reconstructions (MPR) and 20 sagittal MPRs through the patellofemoral joint.   3 - Measurements   -   1st acquisition: .   TT-TG distance .   lateral facet inclination angle .   femoral anteversion, external tibial torsion .   patellar tilt with quadriceps relaxed     -  2nd acquisition .   patellar tilt with quadriceps contracted   -   Desired presentation format: .   large CT film format with 6 images per film. The 3 superimposed images should be presented with and without measurement values.

Conclusion

 

Deepening trochleoplasty is indeed a much more etiological option than so-called elevating trochleoplasty. Its biomechanical effect has been clearly demonstrated by Amis.2 It is best suited for knees with significant prominence of the trochlea. Indications are rare. The learning curve is long and likely arduous as it is a challenging and technically demanding procedure. It is indicated in knees with abnormal patellar tracking or with Type B or D trochlear dysplasia.

 

Objective patellar instability is a multifactorial condition. All anatomic abnormalities must be identified and quantified. Three radiographs are required for planning: an AP view, a true lateral view with perfectly aligned femoral condyles for proper evaluation of the trochlear dysplasia, and a Merchant view. CT scan will provide valuable information if performed using the described protocol.

Last but not least: preoperative planning should be performed using the well-known "Menu à la carte" to address each of these abnormalities individually.

  

Références 1. Albee, F.: Bone graft wedge in the treatment of habitual dislocation of the patella. Med Record, (88): 257, 1915. 2. Amis, A. A., Oguz, C., Bull, A. M., Senavongse, W., and Dejour, D.: The effect of trochleoplasty on patellar stability and kinematics: A Biomechanical Study in Vitro. J Bone Joint Surg Br, 90(7): 864-9, 2008. 3. Dejour, D., and Allain, J.: Histoire naturelle de l’arthrose fémoro-patellaire isolée. Rev. Chir. Orthop., 90 1S69-1S129 suppl. au N°5, 2004. 4. Dejour, D., and Le Coultre, B.: Osteotomies in patello-femoral instabilities. Sports Med Arthrosc, 15(1): 39-46, 2007. 5. Dejour, D., and Vasconcelos, W.: Archivio Di Ortopedia e Reumatologia, La femoro-rotulea Oggi novita? e conferme Indice. La Trocleoplastica: indicazioni, tecnica e risultati, 119/1, 2008. 6. Dejour, H., Walch, G., Neyret, P., and Adeleine, P.: [Dysplasia of the femoral trochlea]. Rev Chir Orthop Reparatrice Appar Mot, 76(1): 45-54, 1990. 7. Dejour, H., Walch, G., Nove-Josserand, L., and Guier, C.: Factors of patellar instability: an anatomic radiographic study. Knee Surg Sports Traumatol Arthrosc, 2(1): 19-26, 1994. 8. Donell, S. T., Joseph, G., Hing, C. B., and Marshall, T. J.: Modified Dejour trochleoplasty for severe dysplasia: operative technique and early clinical results. Knee, 13(4): 266-73, 2006. 9. Fithian, D. C., Paxton, E. W., and Cohen, A. B.: Indications in the treatment of patellar instability. J Knee Surg, 17(1): 47-56, 2004. 10. Goutallier, D., Bernageau, J., and Lecudonnec, B.: [The measurement of the tibial tuberosity. Patella groove distanced technique and results (author’s transl)]. Rev Chir Orthop Reparatrice Appar Mot, 64(5): 423-8, 1978. 11. Masse, Y.: [Trochleoplasty. Restoration of the intercondylar groove in subluxations and dislocations of the patella]. Rev Chir Orthop Reparatrice Appar Mot, 64(1): 3-17, 1978. 12. Neyret, P., Robinson, A. H., Le Coultre, B., Lapra, C., and Chambat, P.: Patellar tendon length—the factor in patellar instability? Knee, 9(1): 3-6, 2002. 13. Nove-Josserand, L., and Dejour, D.: [Quadriceps dysplasia and patellar tilt in objective patellar instability]. Rev Chir Orthop Reparatrice Appar Mot, 81(6): 497-504, 1995. 14. Remy, F., Besson, A., Migaud, H., Cotten, A., Gougeon, F., and Duquennoy, A.: [Reproducibility of the radiographic analysis of dysplasia of the femoral trochlea. Intra- and interobserver analysis of 68 knees]. Rev Chir Orthop Reparatrice Appar Mot, 84(8): 728-33, 1998. 15. Rémy, F., Gougeon, F., Ala Eddine, T., Migaud, H., Fontaine, C., and Duquennoy, A.: Reproducibility of the new classification of femoral trochlea dysplasia proposed by dejour: predictive value for severity of femoropatellar instability in 47 knees. J Bone Joint Surg Br, Vol 84-B(Issue SUPP): 43, 2002. 16. Schottle, P. B., Fucentese, S. F., Pfirrmann, C., Bereiter, H., and Romero, J.: Trochleaplasty for patellar instability due to trochlear dysplasia: A minimum 2-year clinical and radiological follow-up of 19 knees. Acta Orthop, 76(5): 693-8, 2005. 17. Servien, E., Ait Si Selmi, T., and Neyret, P.: [Study of the patellar apex in objective patellar dislocation]. Rev Chir Orthop Reparatrice Appar Mot, 89(7): 605-12, 2003. 18. Servien, E., Ait Si Selmi, T., and Neyret, P.: [Subjective evaluation of surgical treatment for patellar instability]. Rev Chir Orthop Reparatrice Appar Mot, 90(2): 137-42, 2004. 19. Servien, E., Verdonk, P. C., and Neyret, P.: Tibial tuberosity transfer for episodic patellar dislocation. Sports Med Arthrosc, 15(2): 61-7, 2007. 20. Tavernier, T., and Dejour, D.: [Knee imaging: what is the best modality]. J Radiol, 82(3 Pt 2): 387-405; 407-8, 2001. 21. Tecklenburg, K., Dejour, D., Hoser, C., and Fink, C.: Bony and cartilaginous anatomy of the patellofemoral joint. Knee Surg Sports Traumatol Arthrosc, 14(3): 235-40, 2006. 22. Walch, G., and Dejour, H.: [Radiology in femoro-patellar pathology]. Acta Orthop Belg, 55(3): 371-80, 1989.