Title: High Tibial Osteotomy
Reference: Hanssen, A.D., Chao, E.Y.S., in Knee Surgery, ed. Fu, Harner, Chapter 55, 1994
This operation has good success when carefully done in a well selected group of individuals.
Points of Interest
The ideal candidate: young ( 65 (probably better off with a TKA). Severe, tricompartmental disease, excessive deformity (> 15 varus), severe ligamentous laxity on the concavity of the deformity, medial or lateral complete meniscectomy, inflammatory arthritis, obesity
– note that hip surgery should be done first if needed, patellofemoral symptoms are not an absolute contraindication, and that there is no real science behind the required arc of motion.
Patient expectations: it is important to note that HTO is recommended for the ability to continue high impact activities which would not be tolerated by a prosthesis – running, tennis, etc. This is a ï¿½buying timeï¿½ operation, as the results after 5-7 years tend to deteriorate. The flipside is that the patient will go through a longer period of rehab, and will not reliably experience the same pain relief as with a TKA.
TKA after HTO
The issue of what the results of TKA are after HTO is not resolved. Certainly, a poorly done osteotomy or one with complications does not do as well after TKA as a primary TKA, but some authors feel that the results are not alot different. Over correction into valgus, and patella infera are two significant problems. Patella infera appears to be caused by contracture of the tendon, making eversion of the patella and exposure more difficult. Also, loss of lateral tibial plateau bone stock is a problem is a large wedge was used to close things down. Soft tissue balancing in the severely overcorrected knee is a nightmare. Despite these problems, some authors suggest that the results of TKA after HTO are no different!
Planning – the rule of 1 mm of wedge per degree correction only really works on a tibia that has a width of 56 mm or less – the average female is 70, the male is 80 mm. If a patient has a short tibia, taking a wedge of 15 mm will shift their tibia over fairly significantly, whereas in a tall patient, this 15 mm wedge will not as effectively bring the centre of the knee in line with the mechanical axis.
Anatomic axis – normally about 5 degrees valgus
Mechanical axis – normally about 1.2 degrees of varus
Results: the long term results are not the greatest – people generally do well for 5-7 years then the percentage of satisfactory results drops off. There are a number of prognostic factors:
1. Age – young active patients who would be poor candidates for a TKA are often able to do much more of the high impact activities that they want to do.
2. Underlying diagnosis – unicompartmental OA is the best; inflammatory arthritidis donï¿½t do as well, and those with medial AND lateral meniscectomies do poorly; prior medial meniscectomy did not adversely affect the results. The best are the young, unilateral OAï¿½s.
3. Patellofemoral joint – moderate or severe patellofemoral OA is bad. There is not much literature to suggest whether HTO is beneficial for the patellofemoral joint.
4. Postoperative alignment – the single most important factor! It is not clear-cut, but it appears that you need to achieve an OVERcorrection to an anatomic valgus of 8-10 degrees. Patients with 7-13 degrees have far better results than those with less than 7 degrees of valgus.