Osteochondritis Dessicans- Primary Fixation using Bioabsorbable Implants.

INTRODUCTION: Osteochondritis dessicans (OCD) is a localized condition where a section of articular cartilage and underlying subchondral bone separate from the joint surface. It is important to diagnose unstable OCD early and fix the fragments primarily as the results of any surgical management at late presentations are guarded. Use of bioabsorbable implants for fixing OCD is recent and we report one such case in grade IV OCD. CASE REPORT: We present a 14 year old girl who came with a history of acute pain, swelling, inability to bear weight on the right knee following a dance practice. MRI showed stage IV osteochondral fragment measuring 20x 8mm lying free. This was primarily fixed with bioabsorbable implants. 10 months follow up showed excellent clinical and functional results.
CONCLUSION: This case highlights the advantages of early primary fixation whenever possible. By far, to our knowledge, this is the first case of successful treatment of stage IV OCD using bioabsorbable implants.

Introduction

Osteochondritis Dessicans (OCD) is a localized condition where a section of articular cartilage and underlying subchondral bone separate from the joint surface. If this involves a weight bearing area it can progress to degenerative joint disease. The condition is found primarily in the knee, ankle and elbow joints. The knee is the most commonly affected, being involved in nearly 75% of cases [1, 2].

They are overuse injuries resulting from repetitive micro trauma. In children, they are seen in athletically active adolescents and 50-80% is seen on poster lateral aspect of medial femoral condyle. 15-20% of the times it is seen on lateral femoral condyle. Repeated stress and altered vascularity of subchondral bone result in localized osteonecrosis. This progresses through the stages of instability, nonunion and fragment separation[3,4].

Acute osteochondral fractures differ from OCD lesions in that they result from single traumatic event. The vascularity is intact and 60-70% of the lesions are in the medial patellar facet. Recent papers report treatment of OCD by internal fixation using bioabsorbable implants [5-9]. Review of literature have shown few papers of stage 1, 2 and 3 lesions of OCD being fixed primarily but this would probably be the first case of stage 4 lesion being fixed primarily by bioabsorbable implants

Case Report

A 14 year old girl who presented with history of acute pain, swelling, inability to bear weight on the right knee following a dance practice. Clinically she had a hemarthrosis and restricted movement of the knee. Radiograph revealed a loose body in the lateral gutter and MRI/CT confirmed that it was an osteochondral fragment measuring around 20 x 8mm from weight bearing area of lateral condyle femur (Fig.1 & 2).

Figure 1

MRI Scan of knee showing a small loose body in the lateral gutter (Arrow)

Figure 2

CT scan showing an osteochondral defect in the weight bearing area of lateral femoral condyle

Considering the age of the patient, size of the fragment and weight bearing area, it was decided to do an open reduction and internal fixation with bioabsorbable implants[10,11].

Arthroscopy was done 9th day after injury and the large defect on the femoral lateral condyle identified. The loose fragment was found in the lateral gutter. According to both Guhl’s classification[12] and Ewing and Voto classification [13] this was a stage IV lesion. It measured 20 x 8mm and consisted of smooth articular cartilage and subchondral bone (Fig. 3). The cartilage was mildly frayed at the edges on one side but the surface looked smooth but pale. This was fixed back to the defect through mini arthrotomy. The raw area was curetted and prepared to accept the osteochondral fragment. A K-wire was used for temporary fixation of fragment. C-arm was not used as the lesion was visible through the arthrotomy incision. 1.5mm bioabsorbable pin and a 2mm bioabsorbable cortical screw were used to securely fix the fragment. The child was kept non weight bearing for 6 weeks.

Figure 3

Osteochondral fragment measuring 20x 8mm

Static Quadriceps exercises were started immediately post-surgery in cylinder cast. The cast was removed after 6 weeks and gentle active and passive knee mobilization was initiated. With this physiotherapy, full range of pain free movements was achieved by 10 weeks post-op. CT scan at the end of 9 months showed good alignment and fixation of the fragment (Fig. 4) and the child resumed dancing by 12 months post-surgery.

Figure 4

CT scan at 9 months post-op shows good union of OCD fragment

Discussion

OCD in adults could be the result of undiagnosed, untreated or conservatively treated juvenile onset osteochondritis. Cahill et al has shown that conservative treatment has failed in 40 out of 92 patients of juvenile OCD [14]. The long term results of conservative or excision of fragments of lateral condyle end up with grade 2 or 3 OA at average follow up of 13 years[15].

Many treatments have been tried for OCD, including removal of the fragment [16], drilling [17-19] and curettage of the crater, Microfracture, replacement of the native fragment with internal fixation, allograft replacement, autograft replacement and autologous chondrocyte transplantation [20].

The treatment of OCD lesions of the knee differ according to the fragment type and age of the patient. Stable lesions in skeletally immature patients are treated with conservative management with good result [21]. Drilling alone resulted in 50% improvement rate in adult form although much better results are reported in children [19,22]. The autologous cartilage transplant technique used in the treatment of OCD lesions has gained great popularity in recent years. This technique is a cartilage transfer method, which increases subchondral bone vascularization that helps the recovery of OCD lesion [23]. Autologous chondrocyte implantation with or without bone grafting has been used with good success rate [20,24,25]. However the technique is done only in few selected centres backed by culture laboratory and is expensive.

Pascual-Garrido et al reported 88% cell viability in detached osteochondral fragments in OCD, thus supporting internal fixation as a good option [26]. Smilie et al introduced the fixation method using wires [27], which was followed by other fixation methods like screws, Herbert screw or Wagner procedure [28]. Herbert screws have shown 93% successful results however the disadvantage is requirement of a second surgery for implant removal [29].

Bioabsorbable pins have been used with good success rate [5-7]. Problems with these smooth pins are high rate of backout and lack of compression and stability [6]. Two kind of threaded devices have been reported to be used for OCD in young children. Tabaddor et al reported use of Threaded bioabsorbable device called “Smart nail’ and reported good outcome in 22 of 24 patients [8]. Camathias et al in recent study reported used of partially threaded bioabsorbable screws with good results in 12 of 13 patients [9]. Thus good results are reported with use of bioabsorbable screws in OCD in children. However both these studies focused on lesion less than stage IV. In study by Tabaddor et al there was one case with grade IV lesion, however this case showed no healing and required repeat surgery with chondrocyte implantation. They did not recommend bioabsorbable fixation for stage IV lesions and suggested use of metal screws for the same. In study by Camathias et al [9] stage IV lesions were excluded from the study probably based on recommendations of Tabaddor et al [8]. Thus in this sense our report is first report of successful treatment of stage IV lesion with partially threaded bioabsorbable screw in a skeletally immature patient. This was possibly because of early presentation, prompt diagnosis, immediate surgical intervention and an adequate stable fixation achieved by use of a combination of screw and a pin. We feel adequate fixation is the key and more than one implant can be used if fixation is not stable. Also combination of screw and pin can accommodate for lack of compression by smooth pin and achieve a better fixation. Again in our follow up no complications like screw or pin back out, breakage, or synovitis were encountered. We found bioabsorbable implants to be safe and gives successful result in our case of stage IV OCD.

Conclusion

Internal fixation is a good option for acute OCD even in cases with completely dislodged fragment. Use of bio screw can attain good healing and has advantage of not requiring second surgery for implant removal.

Early fixation of free floating fragment of Osteochondritis Dessicans using bioabsorbable screws achieved good clinical and functional result in our case.