RE: Total Hip Replacement answers

[Guest guest]

Nice summary Dave! I would also warn those of you out

there performing rehab on cementless systems not to push them too hard too fast.

Unlike the cemented systems which are very stable immediately post-op (except

for the soft tissue healing….ie., joint capsule, tendons, etc) the cementless

system gets stronger/more stable over time as they allow for bony in-growth.

If the patient is too active (causing too much stress and micromotion at the

stem-bone interface) there is a chance that instead of bony in-growth a fibrous

in-growth will occur leading to pain and intermittent lameness.

Happy Thanksgiving,

Sherman

Sherman O. Canapp Jr., DVM, MS

Diplomate ACVS

Veterinary Orthopedic &

Sports Medicine Group

10270 Baltimore National Pike

Ellicott City, MD 21042

Phone:

Fax:

http://www.vosm.org

From:

VetRehab [mailto:VetRehab ] On Behalf Of

Levine

Sent: Wednesday, November 26, 2008 12:54 PM

To: VetRehab

Subject: Total Hip Replacement answers

In a cemented THA, the main motions to avoid

post-op are excessive abduction, adduction,

and external rotation because they may lead to implant dislocation (luxation).

Ventral

luxation is more likely in dogs with a prosthetic cup placed in 'closed'

fashion and when the

ventral joint capsule is resected. Dorsal luxation is most common and may be

more likely in

dogs with history of dorsal femoral displacement and in dogs that are amputees

on the

opposite pelvic limb.

In a cementless, it is not different in the sense that the three motions

mentioned above also

predispose to luxation. In addition for cementless stems, excessive stress

(axial / torsion) on

the stem in the early (<4 weeks) postoperative period may lead to subsidence

(sinking/settling in the bone) or stem retroversion.

Dave

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[Guest guest]

Most THR patients do a great job of Rehabbing themselves. Could we as therapists improve outcomes? Probably, particularly in patients with advanced OA or those at higher risk for post-op complications, but we don't have objective evidence of this. In our clinic, THR patients routinely return to high levels of activity (after a period of activity restrictions for healing). THR patients from our clinic have returned to hunting, law enforcement, conformation competition, and national frisbee competitions without the benefit of structured, professional Rehab. For that reason, we do not perform structured Rehab before 6-8 weeks (to allow bony ongrowth or ingrowth, dependent upon the type of prosthesis implanted as well as soft tissue healing and compentency), if ever. Even in the face of significant peri-articular fibrosis that limits ROM peri-operatively, the patients almost always restore full or functional PROM on their own in a short length of time without the benefit of stretches. So, the potential detriments of PROM or stretching in the early phases of recovery outweigh the potential benefits in my experience. (This is in stark contrast to total knee replacements and total elbow replacements but that is an entirely different conversation!) The original question was related to why canine THRs are not as subject to luxation as they seem to be in people. Strict observance of ROM limitations for 2-3 months are required in humans to prevent luxation, dependent upon the surgical approach but usually no flexion >90, no adduction past neutral, and no internal rotation past neutral. To illustrate how easily humans luxate, when I worked at a human orthopedic facility we had a luxation occur in a patient who smoked (AMA) post operatively. There was a low bench outside next to the ash trays. A THR patient sat on the bench (flexed past 90 degrees), then leaned over to put out a cigarette (thus IR, adduction) and caused a luxation to occur. Dogs obviously sit with much more flexion than 90 degrees and aren't concentrating on hip position during transfers and mobility. We see dogs post op day 1 laying on the operative limb, positioned in hip adduction, without luxation. Correct implantation (e.g. no mal-alignment of the components) is the biggest variable preventing luxations. Avoidance of trauma, such as slipping and falling with the limb in full abduction or adduction or external forces (tackled by another dog, HBC, etc.), is the biggest post-operative variable to control to prevent luxation.

Dr. Bill Liska has performed over 1300 THRs; we have discussed the differences in canine and human THR patients. He feels that in addition to the obvious anatomical differences, soft tissue tension plays a signficant role in avoidance of luxations. If you have watched a human THR procedure, reduction of the newly implanted prosthesis is usually relatively easy and doesn't require much force. By contrast, Dr. Liska wants the implant to be firmly seated by the soft tissues with little, or no laxity of the femoral head in the acetabulum. If the patient is in lateral recumbancy, he lifts up on the surgical leg (e.g. perpendicular to the floor) to see if there is any laxity in the joint (Barden's sign). If distraction/laxity is present, a longer femoral neck may be used to increase the tension on the soft tissues, which in turn helps prevent luxations. This potentially can cause some offsetting of the proximal femur which seems to be well-tolerated in dogs but may not be in humans (excessive offsetting in either species can lead to harmful alterations in the biomechanics of the limb, including altered patellar tracking or luxation, but again, another conversation!). Additionally, human THR patients are very intolerant of any leg length discrepancy: no more than 10mm is "acceptable" and 20mm or more is often indication surgical for revision; this may limit the surgeon's optiosn to increase soft tissue tension. I am sure there are other surgical considerations in humans I am not aware of; maybe one of the surgeons on this list can add to the conversation.

Happy Thanksgiving, all! Doyle

To: VetRehab From: scanapp@...Date: Thu, 27 Nov 2008 11:19:10 -0500Subject: RE: Total Hip Replacement answers

Nice summary Dave! I would also warn those of you out there performing rehab on cementless systems not to push them too hard too fast. Unlike the cemented systems which are very stable immediately post-op (except for the soft tissue healing….ie., joint capsule, tendons, etc) the cementless system gets stronger/more stable over time as they allow for bony in-growth. If the patient is too active (causing too much stress and micromotion at the stem-bone interface) there is a chance that instead of bony in-growth a fibrous in-growth will occur leading to pain and intermittent lameness.

Happy Thanksgiving,

Sherman

Sherman O. Canapp Jr., DVM, MS

Diplomate ACVS

Veterinary Orthopedic &

Sports Medicine Group

10270 Baltimore National Pike

Ellicott City, MD 21042

Phone:

Fax:

http://www.vosm.org

From: VetRehab [mailto:VetRehab ] On Behalf Of LevineSent: Wednesday, November 26, 2008 12:54 PMTo: VetRehab Subject: Total Hip Replacement answers

In a cemented THA, the main motions to avoid post-op are excessive abduction, adduction, and external rotation because they may lead to implant dislocation (luxation). Ventral luxation is more likely in dogs with a prosthetic cup placed in 'closed' fashion and when the ventral joint capsule is resected. Dorsal luxation is most common and may be more likely in dogs with history of dorsal femoral displacement and in dogs that are amputees on the opposite pelvic limb. In a cementless, it is not different in the sense that the three motions mentioned above also predispose to luxation. In addition for cementless stems, excessive stress (axial / torsion) on the stem in the early (<4 weeks) postoperative period may lead to subsidence (sinking/settling in the bone) or stem retroversion. Dave

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