Spatiotemporal factors

Several studies have reported significantly decreased gait speed, cadence, step length and stride length at 1 month (Nankaku et al., 2007), 1 year (Perron et al., 2000; Tanaka et al., 2010), and 10 years (Bennett et al., 2008) postoperatively. Although 1 month postoperatively may be too early to identify persistent gait deviations, Bennett et al. (2008) provided strong evidence that spatiotemporal parameters may never return to normal. Conversely Miki et al. (2004) and Nantel et al. (2009) reported that gait speed had returned to that of normal controls at 6 months and 1 year postoperatively. However, the mean ages in these studies were 49 and 52.6 years, respectively, which is younger than usual candidates for THR.

Kinematics

Several studies have observed decreased motion in the sagittal plane about the involved hip, attributing this decrease in range of motion primarily to decreased peak hip extension prior to push-off (Fig. 7.1) when compared with age-matched, healthy controls (Beaulieu et al., 2010; Bennett et al., 2008; Foucher et al., 2007; Perron et al., 2000). Bennett et al. (2008) and Perron et al. (2000) suggested that failure to fully extend the hip during late stance was correlated to decreased gait speed. Several studies have suggested that this decrease in hip extension may be linked to passive resistance or contracture in anterior hip structures (e.g., hip flexors) rather than hip extensor weakness (Miki et al., 2004; Nantel et al., 2009; Perron et al., 2000).

Fig. 7.1 • Demonstrating decreased sagittal plane hip range of motion, mostly the result of decreased hip extension during the late stages of stance

(from Perron et al., 2000).

A significant increase in ipsilateral trunk lateral bending has also been observed during single limb support on the operated limb (Nankaku et al., 2007; Perron et al., 2000) along with decreased peak hip adduction angle (Beaulieu et al., 2010; Perron et al., 2000) when compared with age-matched, healthy controls. Both deviations are considered strategies to decrease demand on the hip abductors to stabilise the pelvis in the frontal plane during single limb stance by moving the centre of mass closer to the axis of rotation (i.e. the hip). Nankaku et al. (2007) concluded that lateral trunk bending led to increased energy expenditures. Beaulieu et al. (2010) also suggest that lateral trunk bending may be an attempt to improve balance.

Kinetics

Coupled with the changes in kinematics several changes in kinetics have also been identified. Perron et al. (2000) and Miki et al. (2004) observed a decreased internal hip extension moment during loading response, between 0 and 20% of the gait cycle, which correlated to the decrease in walking speed. This is consistent with the kinematic findings of decreased hip extension range of motion influencing gait speed, suggesting that hip extensor strength is an important factor in the return to a normal gait pattern. In addition, a decreased internal hip abduction moment during mid-stance also occurred, which suggests weakness in the hip abductors (Beaulieu et al., 2010; Foucher et al., 2007; Perron et al., 2000). However, it has not yet been confirmed whether this hip abductor weakness is due to disuse atrophy from pain avoidance strategies prior to surgery, or the effect of the surgery. The lateral surgical approach to THR does involve the detachment and repair of the gluteus medius, yet many of the subjects studied underwent the procedure using a posterior approach, which leaves the abductors intact (Beaulieu et al., 2010). Studies have also noted a decreased hip external rotation moment which may also be attributed to hip abductor weakness (Beaulieu et al., 2010; Foucher et al., 2009; Perron et al., 2000). This moment was identified as a significant determinant of peak implant twisting moment, which is critical for implant stability (Foucher et al., 2009).

Additional clinical relevance

Considering the longevity of the abnormal gait pattern and hip impairments a re-evaluation of current rehabilitation programmes of 2–3 months is warranted (Nantel et al., 2009). It has been suggested that long-term follow-ups (i.e. 6 months or 1 year) be performed with a goal of restoring normal gait pattern. Restoration of normal gait may help in preventing falls and reducing the risk of injury in more challenging activities (Nantel et al., 2009). Early and long-term intervention should focus on alleviating hip flexor tightness and strengthening of the hip extensors and abductors. Gait retraining may also be helpful in achieving a symmetrical and normal gait pattern, and potentially improve overall outcomes.

Key points

Surgical management

There are several surgical approaches to the management of medial compartment knee osteoarthritis. These include total knee arthroplasty (TKA) replacement, uni-compartment knee replacement and high tibial osteotomy (HTO). The aim of all these methods is to reduce excessive loading on the medial compartment of the knee by correcting varus deformity, thereby reducing pain and improving function. In all surgical procedures the focus is on obtaining the best possible anatomical realignment of the pathological joint, which in turn aims to reduce the knee adduction moments to that of a pain- and pathology-free knee.

Total knee arthroplasty

There is a high incidence of TKAs performed worldwide with 71 527 performed in England and Wales in 2008 (National Joint Registry for England and Wales, 2009), with prevalence expected to increase dramatically between 2005 and 2030 (Kurtz et al. (2007) project 3.48 million annually in 2030 in the USA). The goals of the surgery are to alleviate pain, and restore alignment, stability and range of motion of the knee to improve patients’ quality of life (Ranawat et al., 2005).

These patients typically undergo several weeks to months of rehabilitation following the procedure, thus it is highly important for rehabilitation professionals to understand the implications the surgery has on function. Specific to gait, research has demonstrated that TKA causes changes in both kinematic and kinetic parameters. Most studies have been conducted on patients in the long-term stages of recovery, defined as greater than 6 months postoperatively.

Kinematics

There have been multiple systematic reviews on the kinematics of the knee joint after total knee replacement. There is consistency among the literature that total (overall) knee range of motion is decreased in comparison to controls, with a reduction in the knee flexion during loading response (Milner, 2009) (Fig. 7.3). One systematic review found a range of 9.8–16.0° of knee flexion during the loading response for TKA patients versus 16.0–19.7° for controls (Milner, 2009). The same review found absolute differences of 3.0–11.2° in the range of motion between loading response and peak knee flexion during stance. Additionally, TKA patients often demonstrate reduced knee flexion during swing and usually have a greater knee angle at heelstrike (McClelland et al., 2007; Milner, 2009).

Fig. 7.3 • Knee flexion excursion from footstrike to peak knee flexion during weight acceptance in total knee arthroplasty and control groups across studies.

Kinetics

Kinetic changes at the knee joint have been measured after TKA, particularly in the sagittal plane. Normally, a biphasic moment pattern occurs during the stance phase of gait. An external moment across the knee, which causes extension, rapidly changes to a flexion moment, and then changes again to extend the knee and then flex the knee towards the end of stance (McClelland et al., 2007). Internal moments are generated by the leg musculature to counteract these external moments.

After TKA, this normal biphasic pattern is typically not present (McClelland et al., 2007). Depending on the alignment of the lower limb, a flexion moment or an extension moment may be present throughout the duration of stance. When an external flexion moment is present throughout stance, the quadriceps must generate the internal moment to a greater extent. This is termed the quadriceps overuse pattern. When an external extension moment is present throughout stance, there is an absence of quadriceps activity. This is termed the quadriceps avoidance pattern, which is typically discussed with regard to anterior cruciate ligament function (Timoney et al., 1993). Both patterns are common in the TKA population (Fig. 7.4) (McClelland et al., 2007).

Fig. 7.4 • Quadriceps avoidance and overuse patterns.

The quadriceps avoidance pattern is clinically important as the hip or the ankle must compensate for the reduced knee extensor moment. Resultantly, studies have demonstrated that the hip extensor moment is typically increased in TKA patients compared with controls (Mandeville et al., 2007).

Additional clinical relevance

Quadriceps strength has been correlated with functional performance at both 3 and 12 months postoperatively. Yoshida et al. (2008) found that improved quadriceps strength resulted in significantly faster times in the timed up and go test, stair climbing test and 6-minute walk test (p< 0.05).

The available extension range of motion has been found to be a determinant of limb dominance during stance and walking. Harato et al. (2010) compared weight-bearing strategies of individuals with a diagnosis of bilateral arthritis that had undergone unilateral TKAs. Their findings suggest that patients who have sufficient extension range of movement (ROM) during stance utilise the operated lower extremity as the dominant side. However, patients with decreased extension ROM bear more weight on the contralateral limb, which could increase its rate of degeneration (Harato et al., 2010). One factor that could alter kinetics after TKA is patient weight, as compressive forces at the knee joint increase linearly with patient weight gain. One study found significant weight gain was common in the 2 years after total knee replacement. Specifically, 70 of 106 patients who had undergone a TKA gained an average of 6.4 kg (Zeni and Snyder-Mackler, 2010).

Mauer et al. (2005) compared the abilities of healthy age-matched controls to patients with bilateral TKAs in obstacle avoidance. The TKA group success rate in avoiding a suddenly appearing light band flashed on the floor was 30% less than controls. Clearly, this could lead to significant increases in fall risk and might be addressed in rehabilitation (Mauer et al., 2005).

High tibial osteotomy

Jim Richards

HTO is another surgical procedure to alter the bony alignment and reduce the varus angle of the knee joint. The aim of an HTO is to evenly share the load between the medial and lateral compartments of the knee. There are two main types of osteotomy for knee osteoarthritis, an opening wedge and a closing wedge. In an opening wedge, a cut is made in the tibia and the two sides are separated. The wedge-shaped space is filled with a bone graft. In a closing wedge, two cuts are made and a wedge-shaped piece of bone is removed. The two edges are then brought together creating the desired change angle. Both types of operation then require the bone to be fixed, usually with a plate and screws. HTOs are often seen as a way of delaying a total knee replacement in those considered too young. Prodromos et al. (1985) investigated the variable clinical results following HTOs for osteoarthritis of the knee with a varus deformity. They found that clinical success or failure could be predicted by the preoperative measurement of the frontal plane moment of force at the knee, those patients with a high moment having a significantly worse result, with a recurrence of deformity, than those with a low moment. Briem et al. (2007) studied the effects of the amount of valgus correction using HTO for medial compartment knee osteoarthritis. Their results showed that physical function improved significantly overall. However, those subjects whose knee alignment was further away from the group’s postoperative mean tended to improve less than those closer to the mean and have higher adduction moments 1 year after surgery. This again illustrates the importance of correct alignment during surgery and its relevance to adduction moments and clinical outcome scores.

As well as its use in comparative trials between two or more forms of treatment, gait analysis is also commonly used simply to quantify the benefit that a patient receives from a particular type of treatment. In such cases, a comparison may be made with pretreatment data values for that patient and with comparable results from normal individuals. Figure 7.5 shows an example of how the operation of HTO was successful in reducing the external adduction moment at the knee, and changing the varus alignment at the knee from 11° to 1.5°.

Fig. 7.5 • Pre- and post-high tibial osteotomy.

Conservative management of knee osteoarthritis

Conservative management of knee osteoarthritis includes weight loss, patient education, muscle strengthening, bracing (orthotics) and pharmacological intervention. All of these have been shown to be beneficial (Zhang et al., 2008). A recent study of a weight-loss programme in 157 obese patients with knee osteoarthritis decreased their body weight 13.5% in 16 weeks. This corresponded to a 7% reduction in knee joint loading, a 13% lower axial impulse, and a 12% reduction in the internal knee abductor moment (Aaboe et al., 2011). These findings and others (Messier et al., 2000, 2005) have shown that weight loss in obese adults can lead to improvements in function/gait and decreased pain and disability in patients with knee osteoarthritis. In addition, both patient education and muscle strengthening have been found to have positive effects on knee osteoarthritis in improving function, including gait (Zhang et al., 2008).

Orthotic management of knee osteoarthritis has been studied in terms of improvements in joint forces during gait. Knee braces (direct orthotic management) and wedged insoles (indirect orthotic management) are becoming popular orthotic approaches to managing medial compartment osteoarthritis. Both methods aim to influence the external forces applied to the knee, either by directly applying a system of forces or indirectly changing the ground reaction force.

The aims of knee valgus braces are to unload the painful compartment, through bending moments applied proximally and distally to the knee joint, and reducing the varus deformity (Pollo, 1998). Several studies have been conducted into the use of valgus knee braces for medial compartment osteoarthritis, and have reported that patients experience significant pain relief and an improvement in physical function (Hewett et al., 1998; Kirkley et al., 1999; Lindenfeld et al., 1997; Matsumo et al., 1997; Richards et al., 2005) and also a reduction in medial compartment load (Jones et al., 2006; Pollo et al., 2002). The use of valgus bracing in the management of knee osteoarthritis has been a point of debate for some time. Two of the most important biomechanical outcomes measures are the varus angle and the knee adduction moment during loading response. Bracing has been shown to reduce the degree the varus deformity by 3° and reduce the knee adduction moment by 14.5%, providing significant pain relief (Jones et al., 2006).

Another treatment that has been suggested is the use of lateral wedging of the foot. A lateral wedged insole has a thicker lateral border and applies a valgus moment to the heel, attempting to move it into an everted position. Lateral wedging has been found to significantly reduce the peak adduction moment during early stance and reduce pain (Butler et al., 2007; Jones et al., 2006; Keating et al., 1993; Shimada et al, 2006; Toda et al., 2001), however, Kakihana et al. (2007) found some inconsistency in knee varus moment reduction caused by a lateral wedging in knee osteoarthritis in approximately 18% of patients tested.

Research into the use of both knee braces and wedged insoles has shown positive clinical benefits and biomechanical benefits, which include a reduction in the knee adduction moment and varus angle of the knee joint.