Case Reports

Intra-Articular Dislocation of the Patella With Associated Hoffa Fracture in a Skeletally Immature Patient

Am J Orthop. 2015 June;44(6):E195-E198

References

1. Midelfart V. En sjelden luxation of patella. Norsk Magazin for Laegevidenskaben. 1887;4:588.

2. Kramer DE, Simoni MK. Horizontal intra-articular patellar dislocation resulting in quadriceps avulsion and medial patellofemoral ligament tear: a case report. J Pediatr Orthop B. 2013;22(4):329-332.

3. van den Broek TA, Moll PJ. Horizontal rotation of the patella. A case report with review of the literature. Acta Orthop Scand. 1985;56(5):436-438.

4. Flanagin BA, Cruz AI, Medvecky MJ. Hoffa fracture in a 14-year-old. Orthopedics. 2011;34(2):138.

5. Strauss E, Nelson JM, Abdelwahab IF. Fracture of the lateral femoral condyle. A case report. Bull Hosp Jt Dis Orthop Inst. 1984;44(1):86-90.

6. Biau DJ, Schranz PJ. Transverse Hoffa’s or deep osteochondral fracture? An unusual fracture of the lateral femoral condyle in a child. Injury. 2005;36(7):862-865.

7. McDonough PW, Bernstein RM. Nonunion of a Hoffa fracture in a child. J Orthop Trauma. 2000;14(7):519-521.

8. Brady TA, Russell D. Interarticular horizontal dislocation of the patella. A case report. J Bone Joint Surg Am. 1965;47(7):1393-1396.

9. Yuguero M, Gonzalez JA, Carma A, Huguet J. Intra-articular patellar dislocation. Orthopedics. 2003;26(5):517-518.

10. Frangakis EK. Intra-articular dislocation of the patella. A case report. J Bone Joint Surg Am. 1974;56(2):423-424.

11. Nanda R, Yadav RS, Thakur M. Intra-articular dislocation of the patella. J Trauma. 2000;48(1):159-160.

12. Choudhary RK, Tice JW. Intra-articular dislocation of the patella with incomplete rotation--two case reports and a review of the literature. Knee. 2004;11(2):125-127.

13. Chatziantoniou I, Diakos G, Pantelelli M. Horizontal dislocation of the patella. Case report. EEXOT. 2008;59(2):112-114.

14. McHugh G, Ryan E, Cleary M, Kenny P, O’Flanagan S, Keogh P. Intra-articular dislocation of the patella. Case Rep Orthop. 2013;2013:535803.

15. Bankes MJ, Eastwood DM. Inferior dislocation of the patella in the degenerate knee. Injury. 2002;33(6):528-529.

16. Theodorides A, Guo S, Case R. Intra-articular dislocation of the patella: A case report and review of the literature. Injury Extra. 2010;41(10):103-105.

17. Dimentberg RA. Intra-articular dislocation of the patella: case report and literature review. Clin J Sport Med. 1997;7(2):126-128.

18. Morin WD, Steadman JR. Case report of a successful closed reduction without anesthesia. Clin Orthop. 1993(297):179-181.

19. Murakami Y. Intra-articular dislocation of the patella. A case report. Clin Orthop. 1982;171:137-139.

20. Joshi RP. Inferior dislocation of the patella. Injury. 1997;28(5-6):389-390.

21. Garner JP, Pike JM, George CD. Intra-articular dislocation of the patella: two cases and literature review. J Trauma. 1999;47(4):780-783.

22. McCarthy TA, Quinn B, Pegum JM. Inferior dislocation of the patella: an unusual cause of a locked knee. Ir J Med Sci. 2001;170(3):209-210.

23. Manfredini M, Gildone A, Ferrante R, Bernasconi S, Massari L. Unicondylar femoral fractures: therapeutic strategy and long-term results. A review of 23 patients. Acta Orthop Belg. 2001;67(2):132-138.

24. Holmes SM, Bomback D, Baumgaertner MR. Coronal fractures of the femoral condyle: a brief report of five cases. J Orthop Trauma. 2004;18(5):316-319.

25. Nork SE, Segina DN, Aflatoon K, et al. The association between supracondylar-intercondylar distal femoral fractures and coronal plane fractures. J Bone Joint Surg Am. 2005;87(3):564-569.

26. Allmann KH, Altehoefer C, Wildanger G, et al. Hoffa fracture--a radiologic diagnostic approach. J Belge Radiol. 1996;79(5):201-202.

27. Oztürk A, Ozkan Y, Ozdemir RM. Nonunion of a Hoffa fracture in an adult. Chir Organi Mov. 2009;93(3):183-185.

28. Lewis SL, Pozo JL, Muirhead-Allwood WF. Coronal fractures of the lateral femoral condyle. J Bone Joint Surg Br. 1989;71(1):118-120.

29. Arastu MH, Kokke MC, Duffy PJ, Korley RE, Buckley RE. Coronal plane partial articular fractures of the distal femoral condyle: current concepts in management. Bone Joint J. 2013;95-B(9):1165-1171.

30. Westmoreland GL, McLaurin TM, Hutton WC. Screw pullout strength: a biomechanical comparison of large-fragment and small-fragment fixation in the tibial plateau. J Orthop Trauma. 2002;16(3):178-181.

31. Jarit GJ, Kummer FJ, Gibber MJ, Egol KA. A mechanical evaluation of two fixation methods using cancellous screws for coronal fractures of the lateral condyle of the distal femur (OTA type 33B). J Orthop Trauma. 2006;20(4):273-276.

Discussion

In the vast majority of patellar dislocations, the patella dislocates laterally over the trochlear groove. Inferior, or intra-articular, dislocations of the patella are rare. The mechanism of injury is usually a blow onto the patella with a flexed knee. The 2 groups commonly involved are adolescent boys and the elderly.^8,9 In young men, it is thought that lax patellar attachments place adolescents at higher risk for this type of injury.^10-12 While patella fractures and frank extensor mechanism ruptures are uncommon in this age group, the same mechanism of injury can lead to stripping of the deep fibers of the patellar tendon from the superior pole of the patella.^3,13 The intact superficial fibers of the tendon allow the patella to hinge and displace into the joint.¹⁴

Inferior dislocations of the patella are classified into 2 types based on the orientation of the articular surface and the presence of osteophytes.¹⁵ Type I inferior dislocations occur after a direct blow to a flexed knee forces the superior pole of the patella into the intercondylar notch. Type II dislocations are caused by osteophytes on the superior pole of the patella that become wedged in the intercondylar notch and dislocate the patella inferiorly. In type I dislocations, the patella is rotated in the horizontal plane and the articular surface often faces inferiorly, but type II dislocations do not involve rotation of the articular surface. Type II injuries are seen more commonly in the elderly.

Our patient was able to tolerate a closed reduction of the patella after an intra-articular lidocaine injection, and a successful reduction was achieved without great difficulty. However, the majority of reports describe the need for an open reduction of inferior patellar dislocations.^3,8When closed reductions were a success, they were performed under general anesthesia or conscious sedation.³ It is thought that the difficulty of reduction results from the tension of the quadriceps muscle pulling the patella superiorly into intercondylar notch.^11,16 However, successful closed reduction may be more likely in patients with less patellar rotation and entrapment within the intercondylar notch, as well as in patients whose knee is near full extension at presentation.^17-19 Successful closed reduction is also seen in elderly patients, where dislocation is generally caused by less forceful impact and held by osteophytes. In these patients, the knee is commonly held in extension.^12,15,20-22

The fracture pattern seen in this case also shows a rare fracture in skeletally immature patients, with only a few case reports in the literature. Isolated coronal plane femur fractures account for 0.65% of all femur fractures and are usually seen in adults after high-energy trauma.²³ In the skeletally immature, the fracture can occur with lower-energy mechanisms. The typical mechanism is thought to be a shearing force to the femur caused by an axial load to the knee in 90° or more of flexion.^4,24 A CT scan is recommended for better identification of the fracture and to plan treatment.^25,26 Because of their intra-articular nature and tenuous blood supply, Hoffa fractures tend to do poorly with nonoperative treatment and are prone to displacement and nonunion.^27,28 The goal of operative treatment is to obtain anatomic reduction and rigid fixation. While operative fixation techniques are varied, screw fixation with multiple smaller diameter screws has equal pullout strength compared to larger screws and may minimize damage to the articular cartilage.^29-31 By preserving blood supply to the fracture, and allowing for early active mobilization, operative treatment generally provides good long-term functional outcomes in these fracture patterns.²⁴

Conclusion

We describe a case in which the patella of an adolescent boy dislocated inferiorly into the knee joint, with an associated coronal shear fracture of the lateral femoral condyle. To our knowledge, this constellation of injuries has not been reported. For this uncommon injury pattern, we recommend a sequential treatment algorithm to minimize morbidity. We recommend first attempting a closed reduction of the patella with adequate pain control to avoid the morbidity associated with general anesthesia. After a successful reduction, an advanced imaging study (eg, MRI) is advisable to assess for concomitant soft-tissue injuries and preoperative planning, if necessary. The mechanism of injury and force required to cause a patellar dislocation of this nature leaves a high likelihood of other injuries. When a fracture is noted on plain radiographs after reduction, a CT scan can provide important information for planning surgical fixation of the fracture. Even in a skeletally immature patient, the principle of direct reduction and stable interfragmentary fixation of an articular fracture is critical for long-term function, even after a significant trauma to the knee.