Fractures of the distal femur

                                     Fractures of the distal femur 

                                                  Dr KS Dhillon FRCS

Introduction

Distal femur fractures are not common and can be difficult to treat. In the 1960s the common mode of treatment of such fractures was conservative. However with the advent of better fixation devices in the 1970s, surgical fixation of the fractures became the standard mode of treatment. The functional outcome of treatment of such fractures, though many would believe is poor, is according to the literature surprisingly good. Despite the development of post-traumatic osteoarthritis in about a third of the patients the functional outcome remains good in majority of the patients.

Anatomy of the distal femur

The femur becomes trapezoidal in cross section distally where it forms the  knee joint. The medial condyle extends more distal than lateral condyle at the knee joint and the anatomical axis is about 6 to degrees valgus. The posterior halves of the medial and lateral condyles extend posteriorly beyond the posterior cortex of the femoral shaft. In the axial plane the medial femoral cortex slopes about 25 degrees and the lateral cortex slopes about 10 degrees.
The hamstring muscles and the quadricep muscle pull the distal fracture fragment proximally, the adductor magnus displaces it into varus and the gastrocnemius extend the distal fragment.

Epidemiology

Distal femur fractures account for about 6% of all femur fractures and are 10 times less frequent than proximal femur fractures (1).  The most widely used classification for distal femur fractures is the AO/OTA classification (1).

Classification of distal femur fractures.

The AO/OTA classification is widely used to classify the distal femur 

fractures. The fractures are broadly divided into three types. Type A, B and C.

Classification

The distal femur fracture represented by the number 33 and subdivided into three groups:
    1. 33A-- extra-articular metaphyseal fractures which are subdivided into three
         33A.1—simple metaphyseal fracture
         33A.2--- metaphyseal wedge fracture
         33A.3--- metaphyseal complex fracture
    2. 33B-- partial articular fracture which are also divided into three
          33B.1 – lateral sagittal fracture
          33B.2 – medial sagittal fracture
          33B.3--- frontal (Hoffa). Type B3 can be subdivided into three
                          B3.1---anterior and lateral flake
                          B3.2—unicondylar posterior
                          B3.3 – bicondylar posterior

   3. 33C-- complete articular with both condyles detached from the metaphysis.
           33C.1-- articular simple and metaphyseal simple fracture
           33C.2 --- articular simple and metaphyseal multifragmentary fracture
           33C.3 --- multifragmentary articular and metaphyseal fracture
   

Treatment of distal femur fractures

Fractures of the distal femur are fortunately uncommon. They constitute about 0.4% of all fractures and about 3% of femoral fractures[2]. The treatment of these fractures is difficult. In 1966 Stewart et al [3] claimed that "fractures in the distal third of the femur continue to perplex the surgeon. Whether they are transverse, oblique, or comminuted, or supracondylar or intercondylar in a T, Y or V fashion their management still evokes much controversy because of the consistently poor results obtained". However over the years the outcome of treatment has improve with better fixation devices.

Conservative treatment

On rare occasions distal femur fractures can be treated conservatively with a hinged brace and early knee mobilization. Such treatment is useful in patients with undisplaced fractures, in patients who are non-ambulatory and those who are unfit for surgery.

Surgical treatment

Various devices such as external fixators, nails, plates and screws are available to stabilize fractures of the distal femur.

External fixation

External fixators are used to temporarily immobilize the fractured bone till soft tissue healing is adequate for internal fixation of the fracture especially in open fractures. This technique cannot be used for definitive treatment of distal femur fracture because it does not provide adequate stability and it immobilizes the knee joint.

Antegrade intramedullary nailing

Antegrade nailing is indicated in type A extra-articular fractures of the distal femur. It is the method of choice for treatment of segmental femur fractures involving the distal femur.

Retrograde intramedullary nailing

Retrograde nailing is suitable for patients with extra-articular distal femur fracture who have concomitant fracture of the tibia (floating knee) which can be treated though the same approach.
Screw fixation
Type B fractures can be treated with screw fixation through the medial or lateral approach to the condyles. With little or no displacement percutaneous screw fixation is possible. The use of two 6.5 mm screws is  more effective than several 3.5 mm screws for osteosynthesis of these fractures [4]. In the fixation of Hoffa fractures, lag screws placed posterior to anterior provided more stable fixation than anterior posterior placement[5].

Angled blade plate

The 95 degree angled blade plate can be used for stabilization of the supracondylar and intercondylar fractures of the distal femur. The blade plate is preshaped to fit the anatomy of the distal femur.the blade is seated about 2 cm proximal to the knee joint line and the tip of the blade should not protrude beyond medial cortex to prevent damage to the medial structures.

Dynamic condylar screw (DCS)

The 95 degrees DCS is used for similar indications as the angle blade plate. Here the blade is replaced by a cannulated screw which attaches to the plate. The placement is similar to the blade plate.
Plates
There are various plates available to stabilize the distal femur fractures. The older version is the condylar buttress plate and the newer version are the locking condylar buttress plate and the locking compression plate. Plates are useful for fixing more fragile bone especially in the elderly. Biomechanical studies appear to show that locking plates are better than other modes of fixation [6].
A cochrane database systematic review by Griffin et al [7] in 2015, however, found that the currently available evidence for interventions used in treating fractures of the distal femur in adults, is incomplete and insufficient to inform current clinical practice.

Outcome of treatment of distal femur fractures

There is paucity of literature on the long term outcome of treatment of distal femoral fractures.
Egund and Kolmert [8] retrospectively reviewed 62 patients with distal femur fractures at a mean follow up of 5 years. Some of the patients were treated with traction and others had open reduction and internal fixation. They found that displaced bicondylar fractures healed mostly with varus and anterior angulation, medial unicondylar fractures with varus and lateral unicondylar fractures with valgus angulation. Most of the healed supracondylar fractures showed varus angulation. Three patients (5.8%) developed arthrosis in the femoro-tibial (grade I or II) and 14 patients (27%) had OA of  the patellar area. Intercondylar or transcondylar diastasis, or step off of 3 mm or more predisposed the patients to osteoarthritis.
Rademakers et al [9] conducted a retrospective study to analyze the long-term (5–25 years) functional and radiologic outcome of surgically treated intra-articular fractures of the distal femur. They studied 67 consecutive patients with intra articular fractures of the distal femur. Thirty-two patients had a long term follow up with functional and radiological evaluation . At a mean follow-up of 14 years (range 5–25 years), the mean range of knee flexion was 118° (range 10–145°). The Neer score showed good to excellent results in 84% of the patients and HSS score was good to excellent in 75% of the patients. Patients with isolated fractures of the distal femur had significantly better functional scores (Neer/HSS 90 points) compared with those with multiple fractures.
The Ahlbäck score showed a moderate to severe posttraumatic osteoarthritis in 36% of all patients. Despite the OA, 72% of the patients  scored a good to excellent functional result. Ten percent (seven patients) of the patients had deep wound infection and in two patients the infection became chronic and they had knee arthrodesis.
Thomson et al [10] reported a 50% incidence of OA in 22 patients (23 fractures) with type C distal femur fractures who were followed up for a mean period of 80 months (6.6 years). The physical function component of the SF-36 was approximately 2 standard deviations below the US population mean. None of the patients had a subsequent knee replacement.
Another long term follow up study of supracondylar fractures of the femur was published  by Kolb et al (11). They retrospectively studied the outcome in 41 patients with supracondylar fracture of the femur. Eighty percent of the patients were followed up for a mean of 9.5 years (7-12 years). They found that the mean Neer score was 82 points with a score of 89 points in isolated supracondylar fractures and 72 points in patients with associated fractures. The results were good to excellent in 82% of the patients. No mention was made of OA of the knee in this study.

Conclusion

Fractures of the distal femur are not common. They can occur in isolation or may occur in combination with other fractures. The AO/OTA classification of distal femur fractures is widely used and has prognostic significance. Unlike in the past, distal femur fractures are now routinely treated surgically. Various fixation devices are available. There is no evidence of superiority of one device over the other. The functional outcome of treatment is good to excellent in vast majority of the patients.The outcome is better in patients with isolated fractures as compared to those with combination injuries. About one third of the patients develop post-traumatic osteoarthritis. Despite the presences of post-traumatic OA, over 70% of the patients with OA have good to excellent functional outcome.

References

1. Florian Gebhard, Phil Kregor, Chris Oliver. AO Surgery Reference - AOTrauma - AO Foundation at https://www2.aofoundation.org Accessed on 10/11/2016. 
2. Court-Brown M, Caesar B. Epidemiology of adult fracture: a review. Injury. 2006; 37: 691-697.
3. Stewart M J., Sisk T D. Wallace S L. Fractures of the distal third of the femur. J. Bone Joint Surg. 1966; 48-A: 784-807.
4. Khalafi A, Hazelwood S, Curtiss S, Wolinski P. Fixation of the femoral condyles: a mechanical comparison of small and large fragment screw fixation. J Trauma. 2008; 64: 740-744.
5. 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: 273-276.
6. Ehlinger M, Ducrot G, Adam P, Bonnomet F. Distal femur fractures. Surgical techniques and a review of the literature. Orthopaedics & Traumatology: Surgery & Research. 2013; 99(3): 353-360.
7. Griffin XL, Parsons N, Zbaeda MM, McArthur J. Interventions for treating fractures of the distal femur in adults. Cochrane Database Syst Rev. 2015 Aug 13;(8):CD010606. doi: 10.1002/14651858. CD010606.pub2.
8. Egund N and KolmertL. Deformities, Gonarthrosis and Function After Distal Femoral Fractures, Acta Orthopaedica Scandinavica. 2009; 53:6: 963-974.
9. Rademakers MV. Kerkhoffs GMM, Sierevelt IN, Raaymakers EL, Marti RK. Intra-Articular Fractures of the Distal Femur: A Long-Term Follow-up Study of Surgically Treated Patients. Journal of Orthopaedic Trauma. 2004;18 (4): 213-219.
10. Thomson AB, Driver R, Kregor PJ, Obremskey WT. Long-term functional outcomes after intra-articular distal femur fractures: ORIF versus retrograde intramedullary nailing. Orthopedics. 2008 Aug;31(8):748-50.
11. Kolb K, Grutzner P, Koller H, Windisch C, Marx F, Kolb W. The condylar plate for treatment of distal femoral fractures: a long-term follow-up study. Injury. 2009;40(4):440–8. doi: 10.1016/j.injury. 2008.08.046.