Unicompartmental knee arthroplasty versus high tibial osteotomy

Each step you take sends forces that amount to three to eight times your body weight between your femur and tibia, through your knee [1]. Considering this, it is no wonder that the most common type of arthritis is osteoarthritis (OA) of the knee [2]. It is associated with “wear and tear”, injury, and genetic predisposition, and is more likely to occur in people over 50 years old (although younger individuals can also have OA) [3]. Surgical treatment options are available that aim to support improved mobility, reduce pain, and facilitate active lives, including sports—which is a priority, especially for many younger people with knee OA.

Three procedures that seek to surgically manage degenerative OA are HTO, UKA, and total knee arthroplasty (TKA). Successful HTO and UKA can delay a TKA, allowing patients to retain more aspects of their native knee(s) for longer [4, 5].

As Georg Matziolis, Chief Physician at the German Centre for Orthopedics in Eisenberg, Germany, points out, “TKA has the best long-term survival of all the options but the worst functional outcomes and patient reported outcomes measures (PROMs). TKA replaces all compartments (medial, lateral, and patellofemoral) and is therefore indicated for end-stage arthritis in a minimum of two compartments. If arthritis is secondary to systemic diseases such as rheumatoid arthritis, gout, and pseudogout, TKA is recommended even if only one knee compartment seems to be affected.”

Part 1 explored UKA in relation to TKA. This article focuses on similar questions applied to HTO and UKA, comparing these two procedures and examining the indications that would prompt surgeons to select one over the other.

Matziolis reminds us that, “HTO, UKA, and TKA are all viable options to treat degenerative arthritis of the knee but each of these procedures is appropriate for different kinds and degrees of OA.”

Figure 1. TKA, HTO, and UKA are all viable options to address osteoarthritis of the knee. However, there are situations that indicate the selection of one over the others.

HTO

Since 1958, when the procedure was first performed by Jackson [6], and popularized by Coventry [7] starting in the 1960s [8], HTO has been used to treat unicompartmental OA in knees. Whereas UKA and TKA replace elements of the knee joint with prostheses, either in part or in full, respectively, HTO takes a biomechanical approach and is viewed as a realignment procedure. “HTO does not replace the knee joint but optimizes the joint biomechanics by reducing the pressure on one compartment,” says Georg Matziolis. Patient-specific alignment is widely recognized as “the foundation step when planning any surgical intervention” [9].

It is not only a useful treatment for certain cases of single compartment knee OA, but also knee instability. It is sometimes paired with ligament reconstruction (anterior cruciate ligament [ACL]) to address stability issues [10]. Generally, ACL reconstruction accompanies an HTO if there is a posterior slope of more than 12° or severe varus malalignment [11].

Figure 2. Arrows indicate the load distribution before (left) and after (center) the procedure (medial open wedge osteotomy with locked plate osteosynthesis)(right). Used under CC BY-SA 3.0 de license. Source. Image (right) by J Lengerke.

A wedge-shaped cut (see Figure 1) is made in the top of the tibia to change the alignment of the knee by shifting the weight/loading of the arthritic part of the joint to the healthier part (see Figure 2) [12]. It is mostly performed for varus deformities, less commonly for valgus deformities [13]. Preoperative planning using imaging helps surgeons to calculate the size of the wedge/osteotomy needed to correct the weight-bearing axis (see Figure 3). For best results, it is critical that correct alignment is achieved [14]. There is controversy around what constitutes the ideal mechanical alignment but generally the recommended alignment range is between 2° and 6° of mechanical valgus [15].

Figure 3. Line D shows the distance of the proposed osteotomy site and the same length (line d) is drawn over one of the mechanical axes. The distance between the two mechanical axes at this point (line G) indicates what size of the gap at the posterior aspect of the osteotomy should be in order to correct the weight-bearing axis to the correction point. Used under CC BY 4.0 license. Source: Herman BV, Giffin JR. High tibial osteotomy in the ACL-deficient knee with medial compartment osteoarthritis. J Orthop Traumatol. 2016 Sep;17(3):277–285.

Each step you take sends forces that amount to three to eight times your body weight between your femur and tibia, through your knee [1]. Considering this, it is no wonder that the most common type of arthritis is osteoarthritis (OA) of the knee [2]. It is associated with “wear and tear”, injury, and genetic predisposition, and is more likely to occur in people over 50 years old (although younger individuals can also have OA) [3]. Surgical treatment options are available that aim to support improved mobility, reduce pain, and facilitate active lives, including sports—which is a priority, especially for many younger people with knee OA.

Three procedures that seek to surgically manage degenerative OA are HTO, UKA, and total knee arthroplasty (TKA). Successful HTO and UKA can delay a TKA, allowing patients to retain more aspects of their native knee(s) for longer [4, 5].

As Georg Matziolis, Chief Physician at the German Centre for Orthopedics in Eisenberg, Germany, points out, “TKA has the best long-term survival of all the options but the worst functional outcomes and patient reported outcomes measures (PROMs). TKA replaces all compartments (medial, lateral, and patellofemoral) and is therefore indicated for end-stage arthritis in a minimum of two compartments. If arthritis is secondary to systemic diseases such as rheumatoid arthritis, gout, and pseudogout, TKA is recommended even if only one knee compartment seems to be affected.”

Part 1 explored UKA in relation to TKA. This article focuses on similar questions applied to HTO and UKA, comparing these two procedures and examining the indications that would prompt surgeons to select one over the other.

Matziolis reminds us that, “HTO, UKA, and TKA are all viable options to treat degenerative arthritis of the knee but each of these procedures is appropriate for different kinds and degrees of OA.”

Figure 1. TKA, HTO, and UKA are all viable options to address osteoarthritis of the knee. However, there are situations that indicate the selection of one over the others.

HTO

Since 1958, when the procedure was first performed by Jackson [6], and popularized by Coventry [7] starting in the 1960s [8], HTO has been used to treat unicompartmental OA in knees. Whereas UKA and TKA replace elements of the knee joint with prostheses, either in part or in full, respectively, HTO takes a biomechanical approach and is viewed as a realignment procedure. “HTO does not replace the knee joint but optimizes the joint biomechanics by reducing the pressure on one compartment,” says Georg Matziolis. Patient-specific alignment is widely recognized as “the foundation step when planning any surgical intervention” [9].

It is not only a useful treatment for certain cases of single compartment knee OA, but also knee instability. It is sometimes paired with ligament reconstruction (anterior cruciate ligament [ACL]) to address stability issues [10]. Generally, ACL reconstruction accompanies an HTO if there is a posterior slope of more than 12° or severe varus malalignment [11].

Figure 2. Arrows indicate the load distribution before (left) and after (center) the procedure (medial open wedge osteotomy with locked plate osteosynthesis)(right). Used under CC BY-SA 3.0 de license. Source. Image (right) by J Lengerke.

A wedge-shaped cut (see Figure 1) is made in the top of the tibia to change the alignment of the knee by shifting the weight/loading of the arthritic part of the joint to the healthier part (see Figure 2) [12]. It is mostly performed for varus deformities, less commonly for valgus deformities [13]. Preoperative planning using imaging helps surgeons to calculate the size of the wedge/osteotomy needed to correct the weight-bearing axis (see Figure 3). For best results, it is critical that correct alignment is achieved [14]. There is controversy around what constitutes the ideal mechanical alignment but generally the recommended alignment range is between 2° and 6° of mechanical valgus [15].

Figure 3. Line D shows the distance of the proposed osteotomy site and the same length (line d) is drawn over one of the mechanical axes. The distance between the two mechanical axes at this point (line G) indicates what size of the gap at the posterior aspect of the osteotomy should be in order to correct the weight-bearing axis to the correction point. Used under CC BY 4.0 license. Source: Herman BV, Giffin JR. High tibial osteotomy in the ACL-deficient knee with medial compartment osteoarthritis. J Orthop Traumatol. 2016 Sep;17(3):277–285.