ABSTRACT
The superior dislocation of the patella with interlocking osteophytes is a rare condition. A review of the English literature revealed only 12 reported cases. The purpose of reviewing these case reports is to highlight the unusual presentation and the injury mechanism in 2 of our patients, and to present our treatment algorithm. Closed reduction with manipulation of the patella, with or without anaesthesia, was performed without difficulty. We recommend an intermediate step of trying a regional nerve block before proceeding to general anaesthesia. Our patients had full range-of-motion after reduction and they were symptom-free after 3 years of follow-up. There were no recurrent dislocations in our patients.
Key words: exostoses; knee injuries; osteoarthritis, knee; patellar dislocation
CASE REPORTS
Our series covers a total of 4 cases, all of which have been summarised in the Table (patients 13-16). We elaborate upon 2 of these.
Case 1
A 50-year-old man had an industrial accident in which his right knee was hit by a piece of cargo from the front and below. He complained of severe right knee pain and was unable to flex his knee when presented at Queen Mary Hospital, Hong Kong in February 1998. Physical examination showed effusion of the right knee. The patella was high lying and the knee was locked in extension. Tenderness was mainly localised over the infra-patellar region.
Radiographs showed that the patella was superiorly dislocated (Fig. 1). There was interlocking between the osteophytes of the patella and the anterior femoral condyle. Incidentally, there was unfused tibial apophysis which was compatible with Osgood-Schlatter's disease.
Five milligrams of diazepam and 30 mg of pethidine were intravenously administered to the patient. Closed reduction was performed, with hyperextension of the knee to exaggerate the deformity and manipulation of the patella to unlock the osteophytes. The patella fell back to the normal position almost instantaneously, without forceful manipulation.
After the reduction, the knee pain was relieved immediately and active flexion of the knee joint was possible without significant pain. Post-reduction radiographs of the knee joint confirmed the normal alignment of the patella. The patient received a course of physiotherapy, including range-of-motion exercise and muscle strengthening. He resumed his original duty 2 weeks after the injury. He has been followed up for 3 years and his knee joint is pain-free, with no recurrence of dislocation.
Case 2
An 88-year-old woman was admitted to Queen Mary Hospital, Hong Kong in October 1999 for acute exacerbation of arthritic knee pain. Initially she was treated conservatively with rest, analgesics, and physiotherapy. She was discharged uneventfully and was able to walk with a stick. Three weeks later, she was followed up in the outpatient clinic and we found that her problematic knee was locked in extension. She was unable to recall any significant history of injury during those 3 weeks. A lateral radiograph showed a high-lying patella locked in position by the inferior patellar osteophytes and the femoral osteophytes (Fig. 2).
An intra-articular, local injection of anaesthetic and saline was given but failed to unlock the knee. On induction of general anaesthesia, the knee spontaneously unlocked without any manipulation; however, it became locked again in the recovery room. A regional nerve block of the quadriceps enabled the knee to be unlocked and it was protected in a more flexed position using a temporary plaster splint until the patient was fully awake. She has been followed up for 3 years without any further problems.
DISCUSSION
The superior dislocation of the patella is a rare injury around the knee joint. It was first described by Watson-Jones1 in 1956. Since then there have only been 12 reported cases (4 male and 8 female) in the English medical literature up to 2003 (Table).1-11 Female patients were also more dominant in our series. The usual mechanisms of injury include direct impact on the patella,2,3,5-6 hyperextension of the knee joint,1,3,4,7,8 or a combination of the 2. A characteristic of this condition is that the interlocking osteophytes prevent the spontaneous reduction of the proximally displaced patella.2,4,7-9 Hence, it is not uncommon to find marked osteoarthritic changes in the patello-femoral joint. Prominent osteophytes over the inferior pole of the patella as well as on the anterior femoral condyle are usually seen. These indicate knee osteoarthritis, which explains why the usual age of the patients at presentation is between 50 and 60 years. The mean age of all the patients reported was 60 years.
Most patients with this injury can be treated nonoperatively and surgical intervention is rarely indicated. Nearly all the cases (15 out of 16) were reduced by closed method; only one patient required open reduction.8 General anaesthesia is normally not required and sedation is usually adequate for the reduction. Several methods of closed reduction have been proposed, including initial hyperextension of the knee joint followed by passive flexion, or upward pressure over the patella and manipulation.2-4,7,11 We found that the former was safer and more effective because forceful manipulation might result in a fracture of the inferior pole of the patella. General anaesthesia has the advantage of relaxing the muscle and allows a very gentle reduction. There is thus less chance of fracturing an osteophyte and creating an intra-articular loose body. However, we recommend trying a regional femoral nerve block before general anaesthesia, perferably in the induction room (Fig 3). If this intermediate step is successful, then general anaesthesia can be avoided; this is particularly advantageous to older patients.
After the reduction, immobilisation is generally not required unless there are associated theoretical risk factors for recurrent dislocation. These include patella alta, ligamentous laxity, paralytic disorders, and pre-existing genu recurvatum deformity.2,9 One case in the literature reported 3 episodes of recurrent dislocation, which subsequently required arthroscopic debridement of the osteophytes.7 In our series, our third patient probably suffered recurrent superior dislocation of the patella. She did not experience further symptoms after the initial conservative treatment, and the 3-year follow-up did not show any evidence of recurrence.
We suggest that the decision for operation should not be made based solely on radiological appearances. Even a repeated episode of locking is not an absolute indication for surgery. One of the cases reported in the literature that required arthroscopic resection of the osteophytes was simply a case of voluntary dislocation.9
We recommend maintaining the knee in a slightly flexed position during recovery from sedation or anaesthesia. Occasionally, the anaesthetic reversal may not be smooth, and any struggle or muscle spasm may re-lock the knee. Likewise, patients recovering from sedation may struggle, thus hyperextending and re-locking the knee. Our experience showed that it was safe to start mobilisation of the knee joint under the supervision of a physiotherapist. Patients should prevent hyperextension of the knee during the range-of-motion exercise. Most of the patients recovered early without any sequelae.
Our series showed that the true incidence of dislocation of the patella is probably under-reported. Our third case had probably spontaneously reduced on earlier occasions. Radiological appearance alone or repeated episode of locking is not a strict indication for surgical intervention.
CONCLUSION
The superior dislocation of the patella is a rare knee joint injury, the mechanism of which involves hyperextension or direct contusion onto the patella. Although interlocking osteophytes may prevent the dislocation from spontaneous reduction, it can be easily reduced by the closed method under sedation. We prefer a regional nerve block to general anaesthesia because it has a major advantage for older patients. The restriction of motion is unnecessary except during periods of recovery from unconsciousness. The majority of our patients recovered uneventfully.
REFERENCES
1. Watson-Jones R. Fractures and joint injuries. 5th ed. Baltimore: Williams & Wilkins; 1956:792-3.
2. Bartlett DH, Gilula LA, Murphy WA. Superior dislocation of the patella fixed by interlocked osteophytes. A case report and review of the literature. J Bone Joint Surg Am 1976;58:883-4.
3. Wimsatt MH, Carey EJ Jr. Superior dislocation of the patella. J Trauma 1 977;17:77-80.
4. Siegel MG, Mac SS. Superior dislocation of the patella with interlocking osteophytes. J Trauma 1982;22:253-4.
5. Hanspal RS. Superior dislocation of the patella. Injury 1985;16:487-8.
6. Friden T. A case of superior dislocation of the patella. Acta Orthop Scand 1987;58:429-30.
7. Teuscher DD, Goletz TH. Recurrent atraumatic superior dislocation of the patella: case report and review of the literature. Arthroscopy 1992;8:541-3.
8. Rao JP, Meese MA. Irreducible superior dislocation of the patella requiring open reduction. Am J Orthop 1997;26:486-8.
9. Takai S, Yoshino N, Hirasawa Y. Arthroscopic treatment of voluntary superior dislocation of the patella. Arthroscopy 1998; 14:753-6.
10. Scott SJ, Molloy A, Harvey RA. Superior dislocation of the patella-a rare but important differential diagnosis of acute knee pain-a case report and review of the literature. Injury 2000;31:543-5.
11. McWilliams TG, Binns MS. A locked knee in extension: a complication of a degenerate knee with patella alta. J Bone Joint Surg Br 2000;82:890.
DKH Yip, JWK Wong
Department of Orthopaedics and Traumatology, The University of Hong Kong, Queen Mary Hospital, Hong Kong
LK Sun, NM Wong, CW Chan, PY Lau
Department of Orthopaedics and Traumatology, United Christian Hospital, Hong Kong
Address correspondence and reprint requests to: Dr Daniel KH Yip, Department of Orthopaedics and Traumatology, Queen Mary Hospital, 5/F Professorial Block, 102 Pokfulam Road, Hong Kong. E-mail: dkhyip@hku.hk
Copyright Western Pacific Orthopaedic Association Dec 2004
Provided by ProQuest Information and Learning Company. All rights Reserved
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