|
Patellofemoral dysplasia (PFD) is a developmental abnormality of the patellofemoral compartment of the knee. It is a condition that is rarely diagnosed and poorly recognised. There is little about it in the published literature and there is therefore much to be learnt. (Ref X)
As a result of the extensive experience with isolated patellofemoral pathology, the Bristol knee group has become increasingly aware that PFD is often the underlying cause of symptoms.(Ref X)
The dysplasia may affect the patella alone, with the different shapes of patella described by Wiberg.( Ref 1)
Fig 1. Wiberg Gd III Patella
More often there is a combination of patella and femoral abnormalities with the predominant problem being at the trochlea. The severe grades of trochlear abnormality can be recognised fairly easily, but the lesser grades of abnormality are often very difficult to identify even by experienced observers. The Lateral Xray is the key to making the diagnosis as it shows the boney contours of the cartilaginous hump.
Fig 2. Showing the cartilaginous hump
PFD may present in a number of ways, often relating to the age of onset of symptoms and therefore severity of the dysplasia.
In childhood, recurrent atraumatic dislocation of the patella can occur in a severely dysplastic joint, as in habitual dislocation.
 
Fig3. Fig 4.
The less severe forms of dysplasia may present with painful instability (subluxation or dislocation) in a young adult or recurrent dislocation following a moderate traumatic first dislocation.
Isolated secondary osteoarthritis of the patellofemoral joint is the end stage pathology which often presents earlier than its primary idiopathic equivalent in the third of fourth decade.
All too often, however, the previously undiagnosed condition presents with persistent symptoms following failed traditional surgery, including mid-lateral release or a distal realignment.
The history and examination will result in a differential of diagnoses that may be confirmed by further investigations. Often a number of abnormalities may co-exist.
Initial investigation is by x-ray with a standard knee series (standing AP at 30º, standing lateral at 30º and tangential patella view at 30º). The lateral view is the key in trochlea dysplasia with the tangential or skyline view demonstrating the bony morphology of the patella.
The radiological diagnosis of trochlea dysplasia has been described by the Lyon group in one of the few articles on the subject: (Ref 2).
The key features are;
a) Axial Xray, tangential view at 30°: sulcus angle > 145°
b) Lateral Xray: Crossing sign ( base of the trochlea crossing the line of the lateral femoral condyle)
Figure 5. showing the crossing sign
David Dejour (2000) (Ref. 3), has proposed a grading system from A to D although this has a poor inter and intra observer variation.
Special investigations are necessary to develop the management plan. CT scans will allow the objective measurement of the tibial tubercle to trochlea groove offset (TTTG) reflecting the torsional profile of the knee and longitudinal alignment of the extensor mechanism.
CT arthrography or MRI demonstrates the chondral morphology and condition. This will often be significantly different to the osseous morphology. (Ref 4)
 
Figure 6. Figure 7.
TTTG offset CT arthrogram showing a flat trochlear
Arthroscopy is usually required to assess the joint fully and allow a dynamic picture to be created. The arthroscopic findings can be unexpected and the author has found this to be a very useful investigation especially when the joint is viewed through the superolateral portal.
 
Figure 8. Figure 9.
Arthroscopic view from the supero-lateral portal showing the lateral gutter at 0° and 30° of knee flexion.
Acute presentation
The initial management of a patient presenting acutely with patellofemoral pathology is generally non-operative, with rapid rehabilitation within the limit of symptoms. IF their is a loose body this should be removed or reconstructed.
The role of medial patellofemoral ligament reconstruction is not yet clear.
A large proportion of patients will require no further treatment.
Recurrent / chronic symptoms
A number of different operative stategies have been described to treat recurrent patella instability with or without pain. The majority of these involve the creation of an additional anatomical abnormality in an already abnormal often dysplastic joint. The treatment should in our opinion wherever possible aim to correct the anatomical abnormality of the joint based on the investigations to define the precise defect.
In the presence of trochlea dysplasia, a trochleoplasty aims to restore normal anatomy and patellofemoral stability without overloading the medial side of the joint. It may need to be combined with other procedures such as proximal or distal realignment and medial patellofemoral ligament reconstruction should additional malalignment be present. (Ref 6)
There are a variety of procedures falling under the umbrella term trochleoplasty. Not all seek to restore normal anatomy.
Elevation of the lateral femoral condyle or the Albee procedure ( Ref 4) will tend to overload the lateral capsular structures and further anteriorise the patella.
Excision of the chondral hump and interposition of synovium has been described. Although this improves the morphology it is done at the cost of using an abnormal, less robust synovial articular surface.
H Dejour, described the logical operative procedure of deepening the trochlea groove in the presence of a bump. (Ref 2)
The author has been using a similar procedure which has had gratifying results in the short term. It is essential that the procedure is used for the correct indications after detailed assessment of the patellofemoral joint morphology.
 
Fig 11.Severe trochlea dysplasia Fig 12.Elevate an osteochondral flap
 
Fig 13.Continue elevation & remove bone Fig 14.Create new osseous trochlea groove
 
Fig 15.Lay ostochondral flap into the new groove. Fig 16. Secure with vicryl tape
This procedure aims to create a smoothly curved and deepened trochlea groove, with a proximal broad surface in extension, funnelling into a more congruent articulation to capture the patella in flexion similar to the AVON femoral component.
Post operative rehabilitation is evolving and based around early active movement and functional activity.
 
Fig 17. Pre operative lateral Xray Gd II Fig 18. Post Operative Lateral showing
 
Fig 19. Fig 20.
Post-operative pictures of a trochleaplasty with MPFL reconstruction showing smooth tracking of the patella throughout the range of movement compared to Fig. 3 and 4.
References:
- Wiberg G. Roentgenographic and anatomical studies on the patellofemoral joint:
With special reference to chondromalacia patella
Acta Orthop Scand 1941: 12, 319.
- Dejour H, Walsh G, Neyret P, Adeleine P. La dysplasie de la trochlee femorale. Rev Chir orthop 1990: 76, 45-54.
- Dejour D. et al. Francais J Orthop 2000.
- van Huyssteen AL, Hendrix MR, Barnett AJ, Wakeley CJ, Eldridge JD. Carticalge-bone mismatch in the dysplastic trochlea: an MRI study. J Bone Joint Surg [BR] 2006;88-B:698-91
- Mulford JS, Wakeley CJ, Eldridge JDJ. Assessment and management of chronic patellofemoral instability J Bone Jt Surg. 2007; 89-B: 709-716.
- Utting MR, Mulford JS, Eldridge JDJ. A prospective evalutation of trrochleoplasty for the treatment of patellofemoral dislocation and instability. J Bone Jt Surg 2008;90-B:180-5.
- Yamada Y, Toritsuka Y, Yoshikawa H, Sugamoto K, Horibe S, and Shino K. Morphological analysis of the femoral trochlea in patients with recurrent dislocation of the patella using 3-dimension computer models. J Bone Jt Surg. 2007; 89-B: 746-51.
- von Knoch F, Böhm T, BürgiML, von Knoch M, Bereiter H. Trochleaplasty for recurrent patella dislocation in association with trochlear dyslplasia: a 4 to 14-year follow-up study. J Bone Joint Surg 2006;88-B:1331-5.
- Albee F.H. The bone graft wedge in the treatment of habitual dislocation of patella. Med Rec 1915: 88, 257.
Jonathan D.J. Eldridge FRCS (Orth)
Bristol Knee Group.
|
