Orthopedics

Tips & Techniques 

Proximal Fibular Osteotomy: Biomechanics, Indications, Technique, and Results

Lakshmanan Prakash, MS, MCh; Shabir Ahmed Dhar, MS

Abstract

The evidence base is growing regarding proximal fibular osteotomy. Most studies show that the pain relief and improvement in terms of radiology is statistically significant. More understandable biomechanical theories explaining this improvement are appearing. Because it has a low complication rate and is relatively easy to execute, proximal fibular osteotomy should definitely be considered in any algorithm for the treatment of medial compartment osteoarthritis of the knee. [Orthopedics. 2020;43(6):e627–e631.]

Abstract

The evidence base is growing regarding proximal fibular osteotomy. Most studies show that the pain relief and improvement in terms of radiology is statistically significant. More understandable biomechanical theories explaining this improvement are appearing. Because it has a low complication rate and is relatively easy to execute, proximal fibular osteotomy should definitely be considered in any algorithm for the treatment of medial compartment osteoarthritis of the knee. [Orthopedics. 2020;43(6):e627–e631.]

Medial compartment osteoarthritis is a painful and disabling condition. High tibial osteotomy is performed in the setting of symptomatic unicompartmental arthrosis associated with coronal plane malalignment in a stable knee.1 The aim of this procedure is to shift the mechanical axis of the lower limb from the medial to the lateral compartment, thereby reducing the load and contact area over the medial compartment.2 This procedure has been reported on since 1961. In recent years, the literature has been increasing regarding proximal fibular osteotomy, a relatively new procedure for the treatment of medial compartment osteoarthritis of the knee.3–5 Proximal fibular osteotomy produces discernible improvement in the severity of pain. Also, in a statistically significant number of patients, the osteotomy opens up the medial joint space.4,5

Non-uniform settlement of the proximal tibia has been proposed as the cause of the varus deformity and medial compartment osteoarthritis.6 However, a convincing explanation for the pain relief witnessed after proximal fibular osteotomy is still evolving.

This article examines the probable biomechanics of pain relief and reports the results of a large number of cases of me-dial compartment osteoarthritis treated with proximal fibular osteotomy. It also aims to delineate the exact indications for which this surgery can be beneficial.

A Short History of Proximal Fibular Osteotomy

The senior author (L.P.) worked as an orthopedic surgeon in a prison for 13 years. During this time, he discovered that osteotomizing the fibula led to effective pain relief. During prison riots, batons were often used to control unruly prisoners. These batons were to be used below the knee to prevent serious injuries. This often led to fracture of the fibula. Given the closed nature of the prison population, the senior author was able to observe these patients for a prolonged period (up to 10 years). Radiological and clinical improvement was observed in all cases (Figure 1). Meticulous line diagrams supported the observations. Observation and maintenance of records started in 2003 and led to a relatively evidence-based procedure during 15 years.3–5 Although the senior author has popularized the procedure, Hara et al7 mentioned proximal fibular osteotomy with high tibial osteotomy in a different context in 1994.

Anteroposterior radiographs of a patient who sustained a fibular fracture on the right side during a prison riot. Several years later, the injured side (A) showed a maintained medial joint space compared with the uninjured side (B).

Figure 1:

Anteroposterior radiographs of a patient who sustained a fibular fracture on the right side during a prison riot. Several years later, the injured side (A) showed a maintained medial joint space compared with the uninjured side (B).

Biomechanics

The fibula is a constrained bone that carries up to 17% of the weight going through a leg in stance phase. Ogden8 classified variations of the proximal tibiofibular joint into oblique and horizontal types. Anatomic and radiological surveys showed that the inclination of the joint surface varied from 0° to 76°. The classification was based on the inclination of the joint surface: joints with greater than 20° inclination were considered the oblique type and joints with less than 20° inclination were considered the horizontal type.8 Ogden also reported that the proximal tibiofibular joint is useful for the dissipation of torsional stresses applied at the ankle and lateral tibial bending moments and tensile weight bearing. Stability of the joint is provided by the ligaments, interosseous membrane, fibular muscles, and distal tibiofibular joint.9

Several theories have been proposed for understanding the effects of the fibular osteotomy.

The 3-Cortex Concept

The construct of the tibia and fibula is such that the medial side is more likely to deform. With age and continuous loading, bones with a large cancellous component compress and deform. For example, with increasing age, the vertebral bodies develop a wedge compression. In a similar manner, the medial upper tibial area has a single cortex support, while the lateral aspect has 3 cortices, 2 being contributed by fibula, a wholly cortical bone. This relative lack of support allows the medial side to compact incrementally over time. Removing 2 cortices laterally via a proximal fibulectomy would allow the 2 sides to be equally supported, preventing further differential settling.

The Leaning Tower of Pisa Concept

The femur can be visualized as a tower standing on the tibia. From the above concept, the medial side of the tibia is soft and the lateral side is harder—something akin to the ground on which the Tower of Pisa was built (Figure 2). The femur leans on the tibia because the medial side is softer. One of the ways to correct this tilt is to harden the soft side by lifting it, which is done during a high tibial osteotomy. Conversely, the hard side can be softened by performing a proximal fibular osteotomy.

The two methods to treat the differential loading and correct the tilt. High tibial osteotomy—lifting the soft side and making it firm (A). Proximal fibular osteotomy—softening the hard side, thus increasing the compaction volume (B).

Figure 2:

The two methods to treat the differential loading and correct the tilt. High tibial osteotomy—lifting the soft side and making it firm (A). Proximal fibular osteotomy—softening the hard side, thus increasing the compaction volume (B).

These hypotheses can explain the opening up of the medial joint space over time. However, the immediate pain relief experienced by a significant number of patients after proximal fibular osteotomy is not as easily understood. The compaction zone concept may offer clarification.

The Compaction Zone Concept

The proximal tibia is made up of trabecular bone. The trabecular bone is spongy and, in some ways, acts as a shock absorber. The trabeculae of the medial side of the young tibia share this shock absorbing function to a greater depth. In contrast, the lateral side has a smaller compaction zone because the fibula does not allow the full depth of the trabecular zone to be used as a shock absorber. Although the medial compaction zone gradually loses its elasticity over time, the fibula “protects” the trabeculae (Figure 3). Once the proximal fibula is osteotomized, the trabecular compaction zone becomes fully available as a shock absorber. It is like inserting a new shock absorber on the lateral side. This may account for the almost immediate pain relief experienced by patients.

The compaction zone on the medial side is larger.

Figure 3:

The compaction zone on the medial side is larger.

Surgical Technique

The surgery is performed under spinal anesthesia. It can also be done under local infiltration of lidocaine deep up to the periosteum and going up to the skin. For patients shorter than 5½ feet, the level is 8 cm below the fibular head. For taller patients, it is closer to 9 cm below the fibular head. The level is effective because the interosseous membrane attached to the proximal fragment of the fibula does not interfere with the biomechanical advantage offered by the fibulectomy.

A dead lateral incision is made along the shaft of the fibula, centered 8 to 9 cm below the head of the fibula. The incision should be at least 5 cm long. The fibular shaft is palpable, and the cleavage between peroneal muscles anteriorly and the soleus posteriorly is used to approach the shaft of the fibula. A 1- to 2-cm segment of bone is removed. With a larger incision and proper retraction, the 2 ends of the bone are visualized. Bone wax is applied to the medulla to stop the bleeding.

Materials and Methods

A total of 149 knee joints in 88 patients were studied. Of these patients, 46 were female and 42 were male. The average age was 56.3 years. The right knee was operated on in 48 cases and the left knee in 40 cases. The remaining cases were operated on bilaterally.

The average follow-up was 23 months (range, 12–87 months). The average pre-operative visual analog scale score was 6.7, while the average modified Oxford score was 54.4.

Preoperative radiographs showed that the mean tibio femoral angle was 181°±1.9°. The mean medial joint space was 1.2±0.7 mm. The mean lateral joint space was 7.2±1.4 mm. The preoperative clinical examination showed that the average range of movement was 136.9°.

Results

At final follow-up, the average visual analog scale score was 2.2 and the average modified Oxford score was 77.

Postoperative radiographs showed that the mean tibio femoral angle had improved to 178°±2.0°. The mean medial joint space had improved to 4.5±2.7 mm, while the mean lateral joint space was found to be 5.2±1.4 mm. The postoperative clinical examination showed that the average range of movement was 137.2°.

As indicated by these data, all of the patients had significant pain relief and improvement of function. Although the radiological changes were not very significant, there was a definite opening up of the medial joint space (Figure 4).

Preoperative (A) and postoperative (B) anteroposterior radiographs. The medial joint space increased in 35% of the cases.

Figure 4:

Preoperative (A) and postoperative (B) anteroposterior radiographs. The medial joint space increased in 35% of the cases.

Complications encountered included neuropraxia in 5 knees, extensor hallucis longus weakness in 4 knees, hematoma at the surgical site in 1 knee, and superficial infection in 1 knee that resolved with antibiotics.

Discussion

Proximal fibular osteotomy is performed to relieve pain and retard the radiological deterioration in knees with medial compartment osteoarthritis. The procedure aims to preserve joints.10–12

The open wedge high tibial osteotomy is ideally performed in patients younger than 56 years with a body mass index of 25 to 27.5 kg/m2, range of motion of at least 120°, and a fixed flexion deformity of less than 5°. The joint should have a low-grade medial compartment osteoarthritis (Ahlbäck grade II). The lateral compartment should be uninvolved, and the Caton-Deschamps index should be more than 0.6.13–15

Proximal fibular osteotomy is an alternative to high tibial osteotomy.4 Studies are increasingly showing that proximal fibular osteotomy can be effective for medial compartment osteoarthritis.16 However, despite the evolution of literature related to proximal fibular osteotomy during the past few years, the exact cause of improvement and the pertinent indications for surgery remain a matter of debate.

Why the load on the condyles of the knee is unevenly distributed is not known. Even in healthy knees, the medial compartment bears 60% to 80% of the load. So far, the mechanism proposed by most studies centers around the non-uniform settlement of the tibial plateau, with medial compartment osteoarthritis, being called stress imbalance syndrome of the knee joint.17,18 The fibulectomy is meant to address this imbalance. The current authors think that redressal of this imbalance, while definite, partly explains the effects of the fibular osteotomy. Baldini et al,19 in a biomechanical cadaver study, found that there was no difference in the pressure in the lateral compartment after proximal fibular osteotomy but there was a statistically significant reduction of pressure on the medial condyle. The current authors believe that the increase in the compaction zone, which makes more trabeculae available for shock absorption, unloads the medial condyle without increasing the pressure on the lateral condyle. This might have prognostic significance for the long-term results of proximal fibular osteotomy.

Other mechanisms have also been suggested. The fibular head is pulled to the distal end through the soleus muscle and peroneus longus to form a lever structure, with the lateral tibial plateau as the fulcrum used to pry the medial femoral condyle to reduce the stress of the medial plateau. Hence, the load of the knee joint is transferred from the medial plateau to the lateral plateau, and the distal femoral mechanical axis is rearranged to relieve the lateral soft tissue tension of the knee joint and stop the osteoarthritis symptoms.20 Some studies have also suggested that this procedure is associated with low intraosseous pressure and pain relief.21 However, these mechanisms are not fully explicable.

Being a relatively new surgery, proximal fibular osteotomy needs specific evidence-based indications. Liu et al4 found that the preoperative Knee Society Score was the sole independent factor associated with the clinical satisfaction of patients. The condyle-plateau angle and the medial joint space were also found to be prognostic. Obvious medial space narrowing and smaller condyle-plateau angle meant greater patient satisfaction. However, it was easier to measure the hip-knee-ankle angle and settlement value, so they were suggested as the main bases for patient selection.22,23

Patients most likely to benefit from proximal fibular osteotomy have predominantly medial compartment arthritis with varus knees; have good lateral joint space on weight-bearing radiographs; have at least a 2-mm gap on antero-posterior stress varus radiographs; are motivated and understand that this procedure buys time and delays knee replacement surgery; and have a body mass index of less than 23 kg/m2.

Conclusion

The evidence base is growing for proximal fibular osteotomy. Most studies show that the pain relief and improvement in terms of radiology is statistically significant. More understandable biomechanical theories explaining this improvement are appearing. Given its low complication rate and relative ease of execution, proximal fibular osteotomy should definitely be considered in any algorithm for the treatment of medial compartment osteoarthritis of the knee.

References

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Authors

The authors are from the Institute of Special Orthopaedics (LP), Palakkad, Kerala, and the Department of Orthopaedics (SAD), SKIMS MC Bemina, Srinagar, Kashmir, India.

The authors have no relevant financial relationships to disclose.

Correspondence should be addressed to: Shabir Ahmed Dhar, MS, Department of Orthopaedics, SKIMS MC Bemina, Srinagar, Kashmir, India 190020 ( shabirdhar@yahoo.co.in).

Received: March 01, 2019
Accepted: August 22, 2019
Posted Online: August 20, 2020

10.3928/01477447-20200812-02

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