High tibial osteotomies (HTO) are often performed to treat medial compartment knee OA in the setting of varus limb malalignment. Indications for HTO include patients less than 65 years of age with isolated medial compartment disease, no ligamentous laxity, and full pre-operative range of motion. Contraindications for HTO include severe medial compartment OA (KL Grade 4 changes), tricompartmental knee OA, and knee arc of motion less than 120 degrees or flexion contracture over 5 degrees.(11) Elevated body mass index (BMI) (over 30) and smoking status have also been found to be risk factors for adverse events after osteotomy including delayed union and/or infection; the presence of elevated BMI and/or smoking should be discussed with patients prior to an osteotomy procedure.(12, 13, 14)

While HTO procedures are typically performed in patients who are younger and active, studies have demonstrated improved functional outcomes after HTO in patients over the age of 50.(15,16) While the improvement in function after HTO may be similar, there is a higher conversion rate to arthroplasty in older patients which is likely related to the extent of unicompartmental knee OA present at the time of index surgery.(17) Significant knee OA at the time of HTO (Ahlback grade 3 or greater) has been associated with poor survivorship defined as revision to TKA.(18,19) The presence of OA in other compartments including both the lateral compartment and patellofemoral compartment as a contraindication to performing HTO for medial compartment OA remains controversial. A recent prospective study of 69 patients with a minimum 3 year follow-up demonstrated no change in clinical outcomes for patients that underwent HTO who had chondral changes between International Cartilage Repair Society (ICRS) grade 0 and 2 in the lateral compartment.(20) Similarly, another study showed there was a higher failure rate of HTO in patients who had chondral changes of ICRS grade 2 or greater in the lateral compartment.(21) With respect to the patellofemoral compartment, a prior study demonstrated mild patellofemoral OA did not affect outcomes after HTO.(22) Furthermore, even in studies that note a progression of patellofemoral OA based on MRI after HTO, the progression of patellofemoral OA was not correlated with outcomes.(15) In addition to patellofemoral OA, changes in patellofemoral height as a result of an osteotomy procedure have been discussed which may additionally contribute to changes in patellofemoral joint forces. While normal patellar height has been demonstrated to result in the lowest patellar contact pressures throughout knee range of motion, patella alta is associated with the greatest maximum contact pressure.(23) With smaller osteotomy corrections, changes in patellofemoral height have been found to be negligible. However, with larger corrections of more than 15 degrees, a biplanar osteotomy can be considered with a descending retro-tubercle cut to avoid any changes in patellar height.(24,25)

HTOs for medial compartment OA can be performed using a medial opening wedge (MOW) or a lateral closing wedge (LCW) technique. (Figure 2) Regardless of the technique used, the post-operative weightbearing line should pass through a point 55% of the tibial plateau width, which corresponds to the lateral tibial spine.(26,27) Each technique (MOW-HTO or LCW-HTO) has distinct respective advantages and disadvantages, however desired technique is often chosen based on surgeon comfort level. With MOW-HTO, the procedure is typically faster with higher precision as the degree of correction is not dependent on the initial osteotomy cut, but on the degree of opening at the osteotomy site. With LCW-HTO, there is no need for bone grafting, and the osteotomy is more stable with less risk of collapse/loss of correction. LCW-HTO may be considered in patients with higher risk of nonunion such as smokers.(8)

In a randomized control trial comparing MOW-HTO and LCW-HTO with an average follow-up of over 7 years, there was a significantly lower conversion to arthroplasty in the MOW-HTO cohort (8%) compared to the LCW-HTO cohort (22%).(28) A lower conversion rate in patients after MOW-HTO compared to LCW-HTO was also seen in a recent systematic review of 33 studies. However, the conversion rate to TKA was significantly lower than the previously mentioned study with 2% for the MOW-HTO group and 5% for the LCW-HTO group.(29) Further analysis is warranted to determine if there is any difference in conversion rates between MOW-HTO and LCW-HTO.

Significant improvements in patient reported outcomes can be achieved with HTO in patients with medial compartment OA with long term survival rates ranging between 90-97%.(30, 31, 32) A recent retrospective review of 339 patients with medial compartment OA treated with MOW-HTO demonstrated significant improvement in mean Knee Society Scores (KSS) and Western Ontario and McMaster University Osteoarthritis Index scores at both 5 and 10 years post-operatively.(21) While much of the literature focuses on the results of MOW-HTO, improvement in both pain and functional outcomes have been reported after using both MOW-HTO and LCW-HTO techniques.(30,33, 34, 35)

High rates of return to sport have been cited in patients undergoing HTO for medial compartment knee OA. In a study of 294 patients who underwent HTO for medial compartment knee OA, there was a 82% return to sport rate with 75% of these patients returning within 6 months.(36) In addition, 44% were able to return to intermediate or high-impact sports.(36) Similarly, in a systematic review of 19 studies involving HTO, 87.2% of patients returned to sports post-operatively with 78.6% returning at an equal or greater level.(37) Analyzing athletes specifically, a recent study of 77 high level athletes with pre-symptomatic Tegner levels of 5.3 found that 75% of patients returned to the same level of high-impact sports.(38)

Furthermore, when comparing HTO to unicompartmental knee arthroplasty (UKA) for medial compartment knee OA, a recent study demonstrated no superiority with respect to patient satisfaction or pain scores when controlling for osteoarthritis grade.(39) In addition, several studies have demonstrated greater return to sport rates in those patients who undergo HTO compared to UKA. A matched cohort study of 50 patients undergoing HTO compared to those undergoing UKA with at least 2-year follow-up demonstrated a significantly decreased time to return to sport in those patients undergoing HTO (4.9 months compared to 5.8 months, respectively). In addition, the sports sub-score and Knee Society Score (KSS) activity scores were significantly higher in those patients undergoing HTO.(40) Lastly, a systematic review of 13 studies that included both pre and post-operative Tegner activity scores demonstrated patients who underwent HTO were more physically active pre- and post-operatively that patients who underwent UKA. While post-operative UKA patients had an overall greater increase in Tegner scores, the scores were still below the pre- and post-operative Tegner scores for those patients who underwent HTO.(41)

HTO conversion rates to TKA have been reported between 21-33% with an increased risk of conversion to TKA observed in patients with more severe pre-operative knee OA.(42, 43, 44, 45) A recent prospective analysis of patients who underwent MOW-HTO for medial compartment knee OA reported patients with KL grade 3 or 4 changers in the medial compartment had a nearly 2 times increased rate of conversion to TKA. Other significant risk factors for conversion to TKA were advanced age, female sex, and elevated BMI.(42) Another study of over 2600 patients analyzing the survivorship of HTO (based on conversion to TKA) reported prior history of arthroscopy and meniscectomy, advanced age, female sex, and higher comorbidities increased the risk of conversion to TKA.(43)

While most studies agree performing an HTO allows patients to achieve a higher rate and quicker time to return to sport, studies vary on the overall survivorship and conversion to TKA between HTO and UKA. A recent analysis of the French National Hospitals Database including over 108,000 patients reported increased revision free survival in patients undergoing HTO (80.6%) compared to UKA (75.8%).(46) However, other studies have reported no statistically significant difference in overall survivorship and conversion to TKA between HTO and UKA.(47) The difference in survivorship between the studies is likely the result of differences between the patient cohorts as higher BMI, female gender, older age, and more advanced arthritis have been shown to decrease survivorship.

As some patients who undergo HTO may be converted to TKA in the future, there are concerns regarding the outcome of TKA after HTO. However, a recent retrospective analysis of 231 TKA performed after HTO reported excellent long-term improvement in clinical outcomes. At 10-year follow-up, the rate of revision after TKA was 10%, and only 3% of patients had findings of aseptic loosening. Of note, patients less than 60 years of age had an increased risk of revision surgery after undergoing TKA.(48) In a recent meta-analysis of 15 studies, there was an increased risk of revision and infection in patients undergoing TKA after HTO compared to those patients undergoing primary TKA. However, when comparing complications and revision rates between TKA after HTO and TKA after UKA, studies have demonstrated lower revision rates in TKA after HTO with equivalent complication rates between TKA after HTO and TKA after UKA.(49,50)