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Why is function better with Hip Resurfacing?
Walking and sports
Unlike THR, hip resurfacing allows athletic people to return to full unrestricted sport. A hip resurfacing mimics the natural hip joint more closely. The load is passed from the femoral component in a more natural fashion to the top of the head, rather than through the THR stem to the femoral shaft (thigh bone). Loading the thigh through a stem feels unnatural to most people and results in limitations.
At least 11 scientific studies demonstrate the superior function of hip resurfacing. Many other studies show no difference. None show the superiority of THR. The studies that show equivalence just place the bar too low. If I place the bar only one foot off the ground, any patient can hop over, and we can erroneously conclude that there is no difference. The three best studies showing hip resurfacing superiority are as follows.
- Pritchett reported on 332 patients in which he had performed a THR on one hip and a Hip Resurfacing on the other. 86% preferred the resurfaced hip. Only 6% preferred the THR.
- Barrack evaluated several hundred matched young patients with THR and Hip Resurfacing with detailed activity questionnaires that took the bar way above standard hip questionnaires typically used in THR research. “When controlled for age, sex, and premorbid activity level, patients with hip resurfacing had a higher incidence of complete absence of any limp, lower incidence of thigh pain, lower incidence of perception of limb length discrepancy, greater ability to walk continuously for more than 60 minutes, a higher percentage of patients who ran after surgery, greater distance run, and higher percentage of patients who returned to their most favored recreational activity.” UCLA Activity scores were also much higher for the resurfacing group.
- Cobb has done numerous gait studies demonstrating that THR and Hip Resurfacing patients walk equally well at slow speeds, but the gait at fast walking speeds is more normal in Hip Resurfacing patients.
Two anecdotes that illustrate these findings are the stories of Bo Jackson, the superhuman athlete who suffered a severe injury to his hip in football. He had a THR and struggled afterward to perform as a designated hitter in baseball. He was unable to play football and baseball, he struggled for 2 years as a designated hitter and retired. In the 23 years since then, he has already undergone 2 revision surgeries as benchmark data would have predicted.
On the other hand, Andy Murray returned to win the European Open men’s singles tennis event 1 year after hip resurfacing and was recently ranked #37 in men’s singles tennis. There is a large gap in physical demands between men's singles tennis and a designated hitter in baseball.
There are two biomechanical reasons why hip resurfacing is more functional. Normal hip bearing size provides near-normal stability. Load transfer to the top of the head is more normal than loading the thigh through a THR stem. We will discuss stability later.
The THR stem is the main reason patients struggle to perform after THR. In typical less-active patients who have THR, approximately 30% report slight or mild thigh pain. 3-5% report moderate to severe thigh pain. This is caused by a load transfer from the stem. This is just with activities of daily living. When patients with THR try to return to impact sports (see Barrack above) they are unable. Many patients have pain due to the abnormal load transfer of the stem to the thigh bone (femur). With impact, the sensation is naturally more pronounced and THR patients are often unable to overcome this discomfort. On the other hand, about 40% of my hip resurfacing patients choose to participate in impact sports, the only limitation is occasionally in distance runners. In some patients running more than 2-3 miles is limited, but many who have the desire are even able to run triathlons, marathons, and even ultras.
If you want to walk normally at fast speeds or if you want to run or play impact sports, you want a hip resurfacing.
Hip resurfacing solves the instability problem we have gotten used to with THR. The bearing size in hip resurfacing is normal. In a THR, the bearing size is much smaller than the natural size making a THR unstable. Chronic instability is the leading cause of revision surgery in THR. 3% of THR dislocate within the first few years and 5% by ten years. Half of these patients develop recurrent instability and require revision surgery, which is only 70% effective in resolving the problem. Hip resurfacing, in my hands, carries a 0.3% dislocation risk and only a 0.04% risk of recurrent instability requiring revision.
The rare cases of hip resurfacing instability are related to patients bending their hip too far or falling before the cut ligaments and muscle envelope has had a chance to heal after surgery (6 months). Unlike for THR, no permanent hip position restrictions are required after 6 months for Hip resurfacing patients. When the muscles and ligaments are healed, near normal hip stability iis present.Yoga, gymnastics, kayaking, rock climbing, ballet, and other high-range-of-motion activities can be resumed as normal without any restrictions or fear of hip dislocations. I have even had a number of patients perform the splits after they are fully healed.