Distal Femur Rotational Osteotomy
Steffen Schröter
INTRODUCTION
Pathogenesis
Several risk factors influence the pathology of patellar instability/dislocation. Besides the widely known risk factors regarding the soft-tissue structures around the knee, bone deformities also influence the pathology.1
The internal torsional deformity of the femur is one of the most important risk factors for patellar instability/dislocation.2
A derotational osteotomy to correct the deformity in the transversal plane (maltorsion) is the surgical treatment of choice.
Cases with patellar instability and internal torsional deformity are congenital deformities and must be distinguished from post-traumatic pathologies.
In contrast to post-traumatic cases, in congenital cases, the correct level of deformity in the transversal plane is not available.
The torsion of the femur has been of interest to research for many years. Internal femoral torsion influences the gait, leading to a so-called toeing-in gait.5 It is well described that the torsion of the femur decreases during the childhood.5 However, an increased internal torsion does not change after the age of 8 years.6 There is no possibility to successfully influence the torsion during the growth with a conservative treatment.5
Theoretically, the osteotomy would be possible at each level of the femur. Dickschas et al7 followed the idea to correct the deformity close to the symptomatic location: Impingement of the hip should be corrected with a proximal femoral osteotomy and patellar instability with a distal femoral osteotomy.
Neither for proximal femoral derotational osteotomy nor for distal femoral derotational osteotomy, an advantage is evident.
In this section, the technique of the distal femoral derotational osteotomy is described.
Classification
A classification of torsion, including the indication of treatment, is not defined.
However, several measurement techniques assessing the femoral torsion have been described.8
Only for the method according to Waidelich et al9 (described below), normative values are published.10
Frosch et al11 recently introduced a classification for patellar instability, including the maltorsion. It recommends several steps of surgery depending on the pathology of the patellar instability, but recommendations when and how to correct the torsion are missing.
Even in a case series of n = 30, distal femoral derotational osteotomies, no clear indication on torsional correction was mentioned.7
In author’s daily clinical routine, a distal femoral derotational osteotomy to treat patellar instability is indicated by an internal torsion of more than 30°. The osteotomy aims to correct the femoral torsion to approximately 20° measured according to Waidelich et al.9
Table 35.1 lists indications and contraindications for distal femoral derotational osteotomy.
TABLE 35.1 Indications and Contraindications for Distal Femoral Derotational Osteotomy | ||||
|---|---|---|---|---|
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EVALUATION
Patient History
The medical history is of the same importance as in most other fields of orthopedic surgery.
Information about the first dislocation, the injury pattern, as well as distinguishing between subluxation and luxation is necessary.
For instance, the following questions should be asked:
Did the patellar dislocation occur while running with slightly internal knee rotation or due to heavy trauma during a football match?
How many times did the patella dislocate and was it always caused by a specific event?
Is pain during gait or just the feeling of instability reported?
Does the patient feel instability combined with subluxation?
Did the patient complain about knee pain or hip pain prior to the first dislocation?
How many and which surgeries were performed in the past?
Is there a hyperlaxity and does the patient report on special positions for sitting? This would be typical for young women.
 Figure 35.1 Physical examination of rotation of the hip as a sign of femoral maltorsion. Prone position: A, Analysis of the internal rotation of the hip. B, Analysis of the maximum external rotation of the left hip. C, Analysis of the maximum external rotation of the right hip. Supine position: D, Analysis of maximum external rotation of the left hip. E, Analysis of the neutral position. F, Analysis of the maximum internal rotation of the hip. Pitfalls: Analysis of the rotation without fixed pelvis. Additional rotation of the pelvis mimics a nonexistent higher rotation. |
Physical Examination and Findings
During inspection, a typical finding is an inwardly pointed knee. However, the inwardly pointed knee is not always the cause of patellar instability or subluxation.
More often, this pathology leads to anterior knee pain; giving-way, stair-climbing difficulties; and the typical gait pattern with marked outward foot rotation.12
The entity of maltorsion in case of patellar instability is more often associated with a high internal torsion of the femur without a high external deformity of the tibia.
This deformity can be examined in knee flexion.
Pathologies in squat position or kneeling must be checked.
The assessment of the range of motion in the hip, knee, and ankle is a standard workflow. However, to examine the rotation in the hip, different methods are possible: supine and prone position (Figure 35.1).
Independent of the technique, increased internal rotation of the hip is almost always present. When analyzing hip rotation in 90° hip flexion, passing the 0° position (internal rotation—0°—external rotation) and having internal and external rotation is usually not a problem. This is a concern in cases with post-traumatic maltorsion.
In author’s experience, if rotation more than 0° (beyond neutral) is not possible externally or internally, the patient will have problems during the gait.
The patellar tracking should be examined in supine position. During knee bending, the patella often starts from lateral at the lateral condyle (subluxation) (Figure 35.2; also see Figure 35.4) and moves to medial distal. Patients complain about pain and an inconvenient feeling.
 Figure 35.2 Physical examination of the knee. Examination of the patellar tracking. The patella is in subluxation (A) and centers during knee bending (B). |
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