Determination of the postoperative limb alignment following a high tibial osteotomy in patients with uni-compartmental knee osteoarthritis, review article

Abstract

Objectives

High tibial osteotomy is an established surgical procedure for treatment of mal-aligned Varus knees due to medial compartment knee osteoarthritis. Aims are to evaluate whether post-operative axial alignment achieves good long-term results.

Methods and results

Literature search done and studies with a follow up period of 2 or more years were included. The mean postoperative mechanical axis varied widely from 3 to 16° with significant differences between the studies.

Conclusion

The results suggested that medial knee osteoarthritis can be treated successfully with HTO. The post-operative valgus angle should be between 3 and 13° of valgus to achieve good long-term results.

1. Introduction

Osteoarthritis (OA) of the knee is a chronic degenerative disease characterised by knee pain, short lived morning stiffness and functional limitation in association with physical signs of crepitus, restricted movement and bony enlargement.¹ It is one of the most common disabling joint conditions with a global presence, and one of the leading causes of health burden and economic loss to the society.² It is estimated that about 4.1 million people in the UK, and 9.3 million people in the USA above the age of 45 years are suffering with osteoarthritis of the knee.^3,4

The pathogenesis of primary OA of knee is multifactorial, but certain predisposing factors consistently associated are age, obesity (overweight), previous knee trauma, female gender, overuse, misalignment and genetics.5, 6, 7, 8 Though there is limited evidence of a OA incidence and axial mal-alignment, there is evidence of a clinical correlation of axial mal-alignment and progression of early OA to advances OA.⁹

Varus axial mal-alignment causes unequal weight distribution and altered dynamics of the muscles leading to preferential degeneration of the medial compartment. The altered dynamics of the muscles acting across the joint further increases the wear and tear in the medial compartment leading to further misalignment and angular deformity.^10,11 Thus, a circular vicious cycle (Fig. 1) is created which can be potentially interrupted by correcting the altered biomechanics so that load can be transferred from the diseased to the relatively healthy part of the knee.¹²

Fig. 1.

The circular reasoning of unicondylar arthrosis.¹²

Presentably there is no known cure for OA. Total knee arthroplasty (TKA) is the only answer for end stage joint disease. TKA has a good success rate with 80% of patients reporting reduction of pain¹³ and a survivorship ranging from 90% to 95% at 10–15 years.^14,15 Despite this, it has its limitations and is expensive and not many in the developing countries can afford it at present. Younger patients (less than 55 years) have a less favourable outcome because of higher functional demands.16, 17, 18 It fails to meet their expectations of kneeling, squatting, stairs climbing, and leading an active life.¹⁹ Their higher level of activity causes the polyethylene to wear out faster.²⁰

Many non-surgical and less invasive joint preserving procedures aimed at decreasing or balancing the load at the knee are available. Self-management programs, ambulatory aid (e.g. canes and crutches), strengthening low-impact aerobic exercises, weight reduction programs, valgus directing force brace (medial compartment unloader), lateral wedge insoles, and High Tibial valgus producing Osteotomy (HTO) have been described for the early stages of OA.²¹ These procedures prolong the life of a damaged knee, help relieve pain and delay the need for a total knee replacement.

The aim of this study is to review the literature on the indications for high tibial osteotomy and ideal frontal plane postoperative alignment after a high tibial osteotomy.

1.1. Indications of high tibial osteotomy

A High Tibial Valgus Osteotomy (HTO), is a procedure for medial gonarthosis, which aims to realign the mechanical axis, thereby transferring the body weight to the preserved normal side of the knee. But where should the postoperative mechanical axis be, towards the centre or the lateral aspect of knee joint and by how much has been a topic of debate and defined differently by different authors (Table 1). The basic principle of HTO is making an osteotomy in the upper part of the tibia, and either resecting a precise predetermined bone wedge from the convex side of the deformity (close wedge) or inserting a wedge-shaped bone graft on the concave side (open wedge).Which of these surgical techniques is better is also debatable.^22,23 Another way is by gradual distraction using an Ilizarov or external fixator.²⁴

Table 1.

Recommended postoperative limb alignment in various studies in chronological order.

Author	Post-op alignment (anatomical in degrees)	Post op alignment (mechanical-HKA angle in degrees	No. of knees	Years of follow up
Coventry et al. 198543		10	213	16
Insall, Joseph,and Msika 198444	5–14		83	8.9
Hernigou et al.1987,35 Hernigou 199625		3–6	93	10,20
Keene et al.198945	7–13		51	5
J.F.Rudan and Simurda 199046	6–14		79	5.8
Valenti et al.199041		3–8	100	11
Hsu et al.199047		4.9
Yasuda et al.199248	12–16		56	15
Bouharras et al.199449	3–10		118	8
Rinonapoli et al.199850	10–12		60	15
Korovessis et al.199951	6–10		63	12
Aglietti et al.200337	8–15		61	15
Sprenger and Doerzbacher 200338	8–16		76	10
Koshino et al.200442	9		75	15 to 28
Takeuchi et al.200952	10.4		31	3.5
Birmingham et al.200953		8	126	2
Benzakour et al.201039		2–4	224	15
Schallberger et al.201126	10		54	16.5

Given the positive outcome of HTO in the long term it is viewed as a feasible alternative in cases of isolated medial compartmental OA as a way to maintain joint function, relieve pain and gain time when the articular cartilage is not completely worn for relatively young patients who do not want to modify their activity levels.^25,26 The success and popularisation of TKA has decreased the overall role of HTO in the treatment of knee OA.²⁷ However, it has been re-appreciated in sports medicine for the treatment of ligamentous injuries and imbalance.²⁸

An ideal patient for HTO is one with Isolated medial joint line pain, age between 40 and 60 years, body mass index (BMI) < 30, high-demand activity but no running or jumping, varus misalignment <15°, metaphyseal varus of tibia >5°, range of movement of more than 100°, normal lateral and patello-femoral compartments, no defect of the posteromedial tibia, normal ligament balance, non-smoker and some level of pain tolerance.^22,29,30 The possibility to return to a sporting activity can also be an important consideration in the decision-making process for treatment of knee OA.³¹

1.2. Planning the post-operative alignment after a High Tibial Osteotomy (HTO)

The keys to a successful osteotomy are adhering to biomechanical principles, careful selection of patients, precise planning combined with a skilful execution of surgical technique and stable osteosynthesis for early mobilisation.²³

A preoperative gait analysis and assessment of the movement at the hip, knee and ankle are essential. A change in alignment at the knee will also have an influence on the ankle.³²

1.3. Optimisation of correction angle

On a full length weight bearing radiograph with patella facing anteriorly, in a knee with neutral alignment, the mechanical axis (line from the centre of the head of femur to the centre of talus) intersects the tibial plateau near the centre (Fig. 2), with the femoral tibial mechanical axis nearly collinear (178–180°).^9,33 A deviation from this angle causes the knee to be aligned in valgus or varus and shifts the load in the lateral or medial compartment respectively.

Fig. 2.

Mechanical and anatomical axis in a neutral, varus and valgus knee.³⁴

HKA-hip knee ankle axis, FM-femoral mechanical axis, TM – tibial mechanical axis.

A good postoperative alignment yields a good long-term result, but this ideal alignment is disputed and varies widely between studies (Table 1). There is controversy on the ideal postoperative angle of valgus. A knee aligned in excessive valgus can have problems of patellar subluxation, opening of the medial joint line, and a rapid degeneration of the lateral joint cartilage. A neutral alignment can lead to re-progression of deformity, pain, and early failure.^35,36 But is there really a linear correlation between pain and alignment. Studies by W-Dhal et al. and Aglietti et al. found a poor correlation between alignment, pain relief, and self-reported physical function.^27,37 This explains the difficulty in determining the ideal outcome measure and also why a variation exists among studies (Table 1) for the ideal angle of postoperative alignment.

Although many long-term studies on HTO are available, comparing the results of different studies is difficult and challenging because of the different outcome measures used by them. What should be used as an outcome measure, patient self-reported knee scores,^38,39 the radiological correction on post-operative films.^35,40 The early pain relief or its sustainability over the years until when the pain reappears, or when the patient has a TKR.^38,41,42 The issue is controversial as there could be a difference of many years between them. It is in fact quite difficult to measure the long-term outcome of a degenerative disease which will in any way progress over time. Further, long term studies using standardised and validated outcomes including pain function and quality of life are needed with a defined end point.

A summary of the studies on the recommendation of optimal correction angle in chronological order is given in Table 1.

From the table it is obvious that we have a wide range of angles (from 3 to 16°) with significant differences between them. Some studies have stated the angles with reference to the anatomical axis while others have used the mechanical axis (Hip Knee Ankle axis) as the reference line. However, it is possible to convert between the two as there is an offset of 5° between them.

In a study by Sprenger on 76 knees with a follow up of 10 years he determined that a 3–11° of valgus gave the best result (90%survival).³⁸ Valenti et al. and Agletti et al. had best results in terms of survivorship when the angle was 3–8° and 3–9° respectively.^37,41 But this is still a wide range. A significant finding by Aglietti et al. was the lack of relation of survivorship to flexion contracture or lack of full extension which many studies stated were predictive of early failure and a contraindication for HTO.^30,37,50

Hernigou et al. followed 93 knees for a period of 10 years. In his study 68 knees with a postoperative mechanical valgus of less than 3 had reverted to varus, had pain and progression of medial compartment osteoarthritis and a less satisfactory outcome with 17 requiring another surgery. 5 patients with a mechanical valgus angle of more than 6° had progressive degenerative changes in the lateral compartment. 20 knees with a postoperative valgus between 3 and 6° had the best outcome with no pain or progression of arthritis.^25,35 Thus, his study was self-confirming that 3–6° of valgus is the ideal angle and both under correction and over correction have a poor long term result.

Benzakour et al. in a study 224 knees followed for 15 years recommended an ideal correction of 5° of valgus but in his study a good or very good result was obtained in only 42%of patients and the female patients were three times more than the male. No mention was made whether gender had an influence on the outcome of HTO.³⁹ Schallberger et al. in a study of 71 patients followed for a mean duration of 16.5 years reported a good outcome with a mean angle of alignment of valgus at 10°.²⁶ Both of the above are recent studies and were comparing open and close wedge methods of osteotomies. Though they found no difference between the two methods, they had very different recommendations for the postoperative valgus angle. The study by Schallberger et al. though has a good description of the demographics of the patients, but it did not clearly state number of procedures done by an open or closed wedge method.

The above papers mainly concentrated on the effect of change in alignment on the outcome in terms of load distribution and cartilage regeneration but little did they mention about how the muscle and ligaments around the joint affected the progression of knee OA and how the change in alignment affected them. Prodromos et al. found that despite the fact that adduction moment at the knee was reduced following a high tibial osteotomy, patients with a high preoperative adduction moment had a poor function, but he did not state if it could be used as a predictor of outcome.⁵⁴ Briem et al. studied the relation between the change in mechanical axis alignment (MAA) and joint adduction moment and muscle contraction. He concluded that MAA of more or less than 5° lead to a high adduction moment and increased muscle co-contraction which result in a poor long term survival.¹¹ His findings narrowed the controversy to an angle of 5 or less but the sample size was small (16 patients).

The controversies of the effect of the relation of the mechanical axis and weight distribution led to experimental studies with cadaveric knees in the laboratory. Electronic pressure sensors inserted into the cartilage revealed that there is equal stress distribution between the medial and lateral compartment between 0 and 4° valgus which is not affected by either the size of the condyles, baseline tibiofemoral alignment, the body weight or the size of the chondral defect.⁵⁵

A cadaveric study by Agneskirchner et al. stated that a neutral mechanical axis slightly loaded the lateral compartment more than the medial but it also stated that despite a HTO high pressures are still maintained on the medial side in a knee under load if the MCL is intact because the tension in it increases when the alignment changes to valgus. Only after sectioning of the distal fibres of MCL there is decrease in medial compartment pressure.⁵⁶ Addition to this was done by the experiments of Fening et al. who reported that it is only the posterior oblique portion of the MCL which gets taught and results in high contact pressures following an HTO.⁵⁷ Cadaveric studies have their limitation as they lack the tone of the muscles, and the strength and structure of the ligaments can be very different from that of a living person.

Some authors have used the position of the mechanical axis relative to the width of the tibial plateau as a guideline for the amount of correction based on the work of Fujisawa et al. He documented best results when the mechanical axis was somewhere between 30 and 40% from the lateral end of the width of the tibial plateau.⁵⁸ The fujisawa point was subsequently determined to be at the junction of the medial 2/3 (62.5%) and lateral 1/3 (32.5) of the articular surface of the proximal tibia. It is considered to be the point through which the mechanical axis should pass after corrective osteotomy.59, 60, 61

The alignment in the frontal plane is just one of the important biomechanical factors in planning an HTO. In fact the planning has to be done in all the 3 planes and should include the sagittal mechanical axis, the patellofemoral joint, the posterior tibial slope of the knee, orientation of the distal femur and any existing malrotation.^40,62

2. Conclusion

The goal of a high tibial osteotomy is to off load the painful medial compartment of the knee to improve function, preserve the joint and improve the patient s’ quality of life and delay the need for a TKA. Long term results are good if it is properly planned and executed in patients with the right indications. Frontal plane alignment continues to be debatable though a good correlation between the MAA and the load distribution exists as demonstrated by many cadaveric studies.

Some possible causes for a poor outcome include under correction, overcorrection, and a gradual loss of limb alignment resulting from improper internal fixation, osteoporosis, and recurrence of degeneration leading to further varus.

Disclaimer

The authors declare that no part of this study has been taken from existing published or unpublished materials without due acknowledgement and that all secondary materials used herein has been fully referenced.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Authors’ contribution to the study

Gagan Sethi: Literature review, data Analysis, manuscript writing. Ahmed Aljawadi: Literature review & Analysis. Mohammed Elmajee: Literature review & Analysis. Anand Pillai: Literature review & Analysis, Critical review & drafting.