Femoral Head Excision: A Practical Approach to Simplifying This Surgery and Improving Outcomes
M. Glyde, BVSc, MACVSc, MVS, HDipUTL, DECVS
College of Veterinary Medicine. Murdoch University, WA, Australia
At the end of this session you will be able to:
- Identify the surgical landmarks for correct excision of the femoral head and neck
- Position the limb correctly to ensure the correct plane of excision
The dog is positioned in lateral recumbency with the affected leg uppermost. The procedure is simplified if the leg is free-draped so that the stifle and hock joints are within the sterile field and can be manipulated during the surgery by a scrubbed-in assistant.
An incision is made immediately cranial to the greater trochanter. The incision is centered at the level of the trochanter and extends distally about 1/5 of the femoral length and the same amount proximally.
The subcutaneous tissue is dissected on the same line. The fascia between the biceps femoris caudally and the tensor fascia cranially is incised along the same line from the trochanter distally. The cranial edge of the superficial gluteal muscle is incised and separated from the tensor fascia muscle.
The division between the middle gluteal dorsally and the tensor fascia lata muscle ventrally is developed. The line of this division is the ventral edge of the ilium – this will be at right angles to the midpoint of your initial incision.
If you are struggling to find the division between the middle gluteal and the tensor fascia lata due to fat or hemorrhage or edema from trauma palpate the wing of the ilium and draw a line from the ventral edge of the ilial wing to the greater trochanter. This is the line that the ventral edge of the middle gluteal muscle lies on.
The middle gluteal is retracted dorsally to expose the deep gluteal. Both insert on the greater trochanter. The middle gluteal has a muscular insertion onto the greater trochanter while the deep gluteal has a white tendinous insertion. The middle gluteal is much thicker than the deep gluteal.
Blunt dissect between the middle and deep gluteal muscles just cranial to the greater trochanter. Use a Langenbeck or similar blade retractor to retract the deep gluteal dorsally to visualize the tendon of the deep gluteal.
A partial tenotomy of the deep gluteal tendon is then made. The deep gluteal tendon is cut transversely at right angles to the direction of the tendon for ½–2/3 of its width about 5 mm from its insertion on the greater trochanter.
A cut is then made from the dorsal edge of the transverse tenotomy in a cranial direction running parallel with the muscle fibers. This will also be the line of incision along the femoral neck into the joint capsule.
The deep surface of the deep gluteal muscle is loosely attached to the joint capsule of the hip. The deep surface of the deep gluteal muscle is blunt dissected away from the joint capsule.
The Langenbeck retractor is now placed more deeply to retract both the middle and deep gluteal muscles.
You should now be looking at the joint capsule of the hip joint and be able to see the thin capsularis coxae muscle running over the joint capsule.
This is the point where people often get “lost” in the approach. You are looking at the joint capsule covering the femoral head and neck; however, it is not as easy to see as it appears in some of the surgical approaches texts.
Externally rotate the leg and palpate the femoral head. You can feel a curved “groove” which is the dorsal acetabular rim.
Now incise the capsule directly along the head and neck. There are 3 ways you can identify the line for this incision:
- The first and easiest way is that the capsular incision is on the same line as the longitudinal incision through the deep gluteal tendon.
- The second is that it is at the most dorsal part of the femoral head and neck.
- The third is that it runs on the same line as the thin capsularis coxae muscle. Use a scalpel blade and make this capsular incision cutting down on the femoral head and neck.
Continue the capsular incision along the femoral head and neck laterally along the cranial surface of the proximal femur through the origin of the vastus muscles.
Combine sharp (scalpel) and blunt (periosteal elevator) dissection to reflect the joint capsule and associated vastus muscles from the cranial aspect of the proximal femur. The capsular tissue will not elevate and will need sharp dissection with a scalpel blade to elevate it. The vastus muscle will elevate easily with a periosteal elevator if you push at 45 degrees to the bone surface and find the subperiosteal plane.
Reflect the vastus muscles from the cranial surface sufficiently so that you will be able to eventually make the femoral neck cut on a line connecting the medial edge of the greater trochanter with the dorsal edge of the lesser trochanter.
A Hatt spoon curette is used to cut the round ligament and luxate the head. This is the best instrument by far for this part of the surgery as it combines leverage of the femoral head with a cutting tip. The Hatt spoon curette is relatively cheap and much better and easier to use than a “hip disarticulator.”
Cutting the round ligament requires careful force and is made simpler if the surgical assistant is externally rotating the femoral head to tension the ligament as it is being cut. The curette is used like an ice cream scoop.
When the ligament is completely cut, the leg will be able to be externally rotated (supinated) 90 degrees, so that the stifle joint and hock joint are perpendicular to the table and the femoral head will “pop out” out of the acetabulum (move laterally).
If you have not completely cut the round ligament you will not be able to externally rotate the leg 90 degrees and the femoral head will remain partly tethered to or within the acetabulum.
The femur is externally rotated so that the stifle is at 90 degrees to normal. Continue to blunt and sharp dissect the joint capsule/vastus muscles so that you can palpate the lesser trochanter. Elevation on the medial aspect of the femur is important to achieve this and now the femur can be externally rotated 90 degrees; this is much easier than before the ligament was cut. Keeping the scalpel blade inside the joint capsule and in contact with the bone as you elevate the medial capsular tissue prevents any iatrogenic damage.
Push a blunt elevator or other blunt instrument ventral to the gluteal tendon insertion on the greater trochanter to identify where the medial edge of the greater trochanter is. Make a mark on the bone at this point.
The lesser trochanter is on the caudal edge of the medial aspect of the femur and is the point of insertion of the iliopsoas muscle. Palpate either the lesser trochanter or the tubular insertion of the iliopsoas muscle on the trochanter so that you can make a mark on the cranial surface of the femur at the dorsal edge of the lesser trochanter. In some dogs you can visualize the tendon of insertion.
If you can’t palpate either the tendon or the lesser trochanter, it is probably because you have not elevated the medial capsular tissue far enough ventrally. Progress this elevation if necessary until you can confidently identify the lesser trochanter.
Mark a line on the cranial surface of the femur connecting the medial aspect of the greater trochanter with the dorsal aspect of the lesser trochanter. Ensure the capsule and vastus is reflected sufficiently to achieve this.
Ensure your assistant is holding the femur at 90 degrees external rotation (supination). This is critical to achieving the correct plane of excision and limiting the amount of rasping you need to do after the excision.
The assistant can ensure the leg is externally rotated 90 degrees by using the stifle joint and hock joint as “handles” and ensuring that they are both held perpendicular to the table/floor.
The assistant needs to focus on this while you complete the excision. The most common mistake is for the assistant to allow some internal rotation of the limb during the cut. This inevitably leads to insufficient neck being removed with an angular piece of bone remaining on the caudal aspect of the neck, which then needs to be removed. It is your responsibility because they are working under your direction.
A sagittal saw with a fine sharp blade is the best instrument to make the cut in the femoral neck. It has the advantage of accuracy, lack of propagation into fracture of the caudal part of the neck and it leaves a smooth surface. Provided the cut plane is correct, there is no need to rasp an ostectomy made with a sagittal saw. A good sagittal saw is one of the best pieces of equipment to simplify this surgery.
The other alternative if a sagittal saw is not available is an osteotome. This is not as good as a sagittal saw as it creates a rougher cut necessitating rasping to a smooth surface. It also has the tendency to cause small fractures of the caudal surface of the femoral neck. This is less likely with a sharp osteotome.
It is important to note the difference between an osteotome and a chisel. Chisels are not suitable for bone surgery. Osteotomes have a symmetric or equilateral triangular tip and cut in the direction that the shaft is aimed. Chisels have an asymmetric tip or right angle triangular tip and do not cut in the direction the shaft is aimed.
The importance of using a sharp osteotome of an appropriate size for the animal can’t be understated.
What about Gigli wire? This needs to be properly placed without entrapping caudal soft tissues and has the disadvantage that when it is placed under tension to make the cut, it tends to migrate medially to the narrowest part of the neck, which is usually the mid part of the neck. In doing so this leaves a significant part of the femoral neck that is not removed. Insufficient or partial removal of the femoral neck is one of the main causes of postoperative morbidity and poor long-term function after excision arthroplasty.
Confirm that your assistant has the leg externally rotated at 90 degrees – the stifle and hock joints should be perpendicular to the table.
Place the sagittal saw or osteotome on the line marked on the cranial femur between the greater and lesser trochanters.
Ensure that the saw or osteotome blade are perfectly vertical/perpendicular to the table. By doing this you are cutting through the femoral neck in the direction of the acetabulum. The acetabulum is medial to the femoral neck and so is protecting the neurovascular structures around the hip joint from the blade.
Commence the cut and concentrate on keeping the sagittal saw blade or osteotome blade “vertical to the world”/perpendicular to the table and on the line you marked between the medial edge of the greater trochanter and the dorsal edge of the lesser trochanter. Provided that you stay perfectly vertical and, on the line, and that your assistant keeps the leg externally rotated at 90 degrees, you will have made the cut in the correct location removing all of the femoral neck and the femoral head.
An excision arthroplasty rasp, which is designed for this task, is used to smooth the ostectomy if necessary. Typically this is unnecessary with a sagittal saw but is usually necessary with an osteotome.
Take care to completely close the joint capsule over the acetabulum as this is important in interposing thick fibrous tissue between the acetabulum and the femur. The rest of the soft tissues are closed as described in standard surgical texts.