Distal Femoral Osteotomy for Patella Luxation

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Distal Femoral Osteotomy for Patella Luxation

Ian Gordon Holsworth and Kirk L. Wendelburg

22.1 Introduction

Corrective osteotomies of the distal femur as part of the surgical technique for addressing congenital patellar luxation have become commonplace for some veterinary orthopedists over the past 10 years. Distal femoral corrective osteotomy (DFCO) has been reported as a successful surgical method for the treatment of the excessive distal femoral angulation that can play a role in patellar luxation. While several methods exist for performing a DFCO, they can be divided into closing or opening wedge osteotomies/ectomies. The use of tibial plateau leveling osteotomy (TPLO) jigs, intramedullary pins, interlocking nails, various plating systems, and Ilizarov fixators, have been reported in the past as techniques to help control, manipulate, and stabilize the osteotomies.

The realization that valgus and varus deformities of the distal femur may contribute to quadriceps complex malalignment and predispose the patella to luxation has changed our understanding of patellar instability and forced the development of presurgical imaging and assessment of femoral anatomy. Many individual variations in the technique of distal femoral (corrective) osteotomy (DFO or DFCO) are present. The major differences lying in presurgical planning, intraoperative use of bone jigs, osteotomy technique, correction of femoral torsion if present, medial, or lateral or combined bone plate application site and choice of implant. The use of locking plates and screws is common with the DFO procedure with several options available to the orthopedic surgeon.

22.2 Anatomy

The normal canine femoral diaphysis has a slight caudal curve in the mid‐sagittal/median plane and a slight medial curve in the coronal/frontal plane. While the normal reference range of anatomic angles have been investigated, documented, and published [1], some less documented variation exists, particularly in the chondrodystrophic breeds. It has been postulated that with increased degrees of distal curvature, the tracking of the patellar mechanism is affected and luxation due to malignment across the stifle joint may result. Distal torsion of the femur is also recognized as influencing femoral condyle alignment and patellar stability. The attachment location of the straight patellar ligament (i.e. patellar tendon) on the proximal tibial tuberosity of the tibial crest also plays a significant role in quadriceps‐patellar complex alignment. The term tibial torsion is applied to varying degrees of abnormal tibial conformation with the end result being variations in the medial or lateral location of the tibial tuberosity.

In patellar luxation, patients the surgeon should attempt to assess the location and degree of skeletal malalignment pre and intraoperatively to allow adjustment of the anatomical malalignment into a normal range. The presurgical imaging techniques that have been utilized for this purpose include both radiography and computed tomography. Debate exists concerning which of these techniques is best suited for surgical assessment, how the patient should be positioned for these studies, and what degree of abnormal angulation justifies a corrective osteotomy. Publications investigating the different techniques are available for review by the individual surgeon [110].

22.3 Surgical Approach

Surgical access to the femur is from a lateral or medial approach. Both approaches have their place in both fracture repair and corrective osteotomies, and both approaches have similar but distinct challenges.

The lateral approach is performed by incising the biceps femoris fascia adjacent to the vastus lateralis m. and reflecting the vastus lateralis m. cranially to expose the bone surface. In the proximal femur, this is complicated by the presence of the tensor fascia lata and gluteal muscles and distally by the soft tissues associated with the stifle joint. The exposure is normally continued distally adjacent to the caudal line of the vastus lateralis m. with incision into the joint capsule to open the joint and allow medial luxation of the patella. The aim of the approach is to expose the complete condylar surfaces and mid to distal femur in the cranial aspect. Incision and retraction of the joint capsule cranially is necessary to achieve this aim.

The medial approach to the femur is made by initially incising the fascial connection between the cranial and caudal sartorius muscles. This fascial connection is distinct in canines but nonexistent in felines, requiring a muscle‐splitting technique. Once the sartorius muscles are separated and retracted, the vastus medialis m. is identified and it can be separated from the neurovascular tract that runs caudal to its caudal margin. This must be performed carefully to avoid iatrogenic damage to these structures. Once the separation between the neurovascular tract and the muscle belly is complete and any perforating vasculature is isolated and ligated as necessary, the vastus medialis muscle belly can be retracted cranially to expose the femoral bone surface. As the dissection proceeds proximally the femoral bone shaft becomes more difficult to isolate effectively and the musculature of the inguinal area impedes good access. Placing deep retractors between the vastus medialis m. and the tendon of the pectineus m. will allow good visualization of the medial and cranio‐medial wall of the femur. If a medial arthrotomy has been performed, the joint capsule incision is continued proximally and laterally to release the patellar complex and allow complete lateral luxation of the patella.

Prior to femoral osteotomy a decision on whether a trochleoplasty is to be performed should be made and completed. Awareness of the depth of the trochlear bone cuts for both a block and wedge‐recession trochleoplasty is important as an excessively deep trochleoplasty may cause issue with distal bone segment bone screws being placed during the implantation phase.

22.4 Ostectomy Technique

22.4.1 Technique 1: Medial or Lateral Femoral Plating with Jig Assistance by IG Holsworth

Once the chosen femoral and stifle approach is completed and the cranial surface of both the intra‐articular and mid to distal femoral shaft is exposed, the intraoperative ostectomy planning can begin (Figure 22.1).

Image described by caption.

Figure 22.1 Intraoperative exposure of the cranio‐lateral aspect of the distal left femur with open arthrotomy and previously performed recession wedge trochleoplasty.

In most cases of distal femoral varus or valgus, the center of rotation and angulation (CORA) is directly proximal to the joint capsule attachment on the cranial aspect of the femur. This can be assessed presurgically on planning imaging, and every effort should be made to perform the corrective osteotomy as close to this location as possible (Figure 22.2a and b).

Image described by caption.

Figure 22.2 (a and b) Full right limb posterior–anterior alignment radiograph (a) and isolated femoral shaft with 16° measured femoral varus. The center of rotation and angulation (CORA) in the frontal plane is seen close to the proximal pole of the patella.

Another factor that must be considered prior to definitive choice of the osteotomy line(s) is the configuration of the locking bone plate that will be implanted. It is wise to place the intended bone plate on the medial or lateral wall of the femur in an approximation of final location to confirm appropriate spanning of the osteotomy site.

An additional consideration that must be entertained is the location of the jig’s bone pins. The distal pin should be placed, in most cases, directly proximal to the cartilage surface in the cranial midline of the distal femur. The final osteotomy location should consider the first distal screw location and alignment below the osteotomy so that drilling of the screw hole does not interfere or contact the jig pin. In the majority of implants, the screw will engage the bone distal to that jig pin. The other issue that must be addressed before jig placement is the proximal jig pin location. It is also imperative that the proximal jig pin be placed in the midline of the cranial femur at a site where the implant spans that pin so that the first proximal plate screw is proximal to the jig pin. Failure to do this can lead to fracture through the jig pin site, as it is not protected by the bone plate if placed too far proximally. Once the jig and plate locations have been determined, the osteotomy location can be finalized and the cranial bone surface is scored to reflect the wedge ostectomy lines (Figure 22.3a and b).

Image described by caption.

Figure 22.3 (a and b) Lateral and cranial view of the distal left femur with an attached Slocum tibial plateau leveling osteotomy (TPLO) jig in the correct location. The lateral aspect closing‐wedge ostectomy is scored onto the bone surface using a sagittal saw to ensure accurate ostectomy performance.

It is also helpful to lightly score the cranial surface of the bone in the midline sagittal plane to allow accurate realignment during ostectomy reduction, and if a torsional adjustment is made, the degree of rotation can be subjectively assessed more accurately.

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Jun 13, 2021 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on Distal Femoral Osteotomy for Patella Luxation

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