Intraoperative Soft-Tissue Balance and Clinical Results (ROM, Function)

Fig. 16.1

Offset-type sensor used in total knee arthroplasty, which enables soft-tissue balance assessment. Left; Fuzion (Zimmer, Warsaw, USA), Right; Attune (Depuy Synthes, Warsaw, USA)

Despite advanced accuracy in bony alignment with the development of surgical instruments, such as the computer-assisted navigation system, obtaining an accurate intraoperative soft-tissue balance remains difficult, especially for young surgeons, as experienced surgeons traditionally address soft-tissue balance through “subjective feel.” Therefore, various offset-type tensor has been developed for use during TKA, which enables soft-tissue balance assessment throughout range of motion (ROM) in the physiological knee after TKA (Fig. 16.2), with reduced PF joint and with the femoral component in place [9]. Therefore, clinical relevance using such intraoperative tensor device is being reported nowadays (discussed in next section).

Fig. 16.2

Gap balancing technique. (a) Extension gap balancing using tensioner. Smaller medial gap was found with tightness. (b) Needle-assisted medial collateral ligament (MCL) release using an 18 gauge needle. (c) Medial and lateral balance and good alignment were acquired after MCL release

Attifield et al. reported that knees balanced in full extension and in flexion (< ±2°) showed a significant improvement in proprioception (p < 0.0005), and soft-tissue balance in both flexion and extension is important to allow satisfactory postoperative proprioception of the knee [10]. Pang et al. reported the TKA group with computer-assisted gap balancing technique had less occurrence of flexion contracture in 2 years after the surgery, less outlier number (anterior tibial translation >5 mm), and less functional score than conventional measured resection technique [11]. Lampe et al. studied clinical outcomes within the first year after computer-navigated total knee arthroplasty (TKA) and reported that higher flexion-extension gap equality values led to statistically significant better KSS-F and KSS-K scores at 1 year [12]. Furthermore, Matsumoto et al. argued that in achieving equalized rectangular gaps at extension and flexion, CR TKA using the gap technique with navigation system is more effective than measured technique, but it does not directly reflect 2-year postoperative clinical outcomes [9].

However, it has been often reported that computer navigation offers little advantage over experienced surgeon judgment in achieving soft-tissue balance in knee replacement. Joseph et al. reported that balancing the mediolateral extension gap in navigated group was superior to non-navigated group (p = 0.001), but no significant difference was found between the two groups in balancing the mediolateral flexion gap or in achieving equal flexion and extension gaps [13]. Widmer et al. reported alignment and component position can be precisely measured intraoperatively with navigation, but intrinsic patient factors remain dominant in determining the clinical outcome at 1 year. Therefore, he reported that intraoperative computer navigation parameters (coronal alignment, ligament balance, range of motion, external tibiofemoral rotation) are predictors of function 1 year after total knee arthroplasty [14].

16.3 Mediolateral Gap Balancing

Mediolateral (ML) balancing is one of the most influential factors in TKA. ML balancing is known to have wider range of tolerance than alignment of lower extremity, but it should be strict [5]. Especially, in PCL substituting type, precise ML balancing is very crucial to knee stability and also influences ROM. Matsuda et al. reported that ROM decreased about 11° when ML balancing is off more than 2° [15].

Most of osteoarthritis patients show some degree of varus deformity, regardless of bone defect. If arthritis progresses in medial side, medial joint capsule and medial collateral ligament (MCL) contracts, which is accompanied by lateral collateral ligament elongate along with flexion contracture in most cases. The ideal goal of ML gap balancing is the balance of bilateral collateral ligaments with 4–7° valgus of tibiofemoral alignment, and it should not be overcorrected. In balancing ligament, osteophyte must be thoroughly removed first, then, releasing the side with contracture is more preferable than reefing elongated ligament of the other side. Liebs et al. reported that pain becomes severe when medial gap is 1.5 mm wider or more than lateral gap in extension [16]. Okazaki et al. argues that lateral gap is greater than medial gap, and this is a compensation mechanism of dynamic stability by iliotibial band [17]. However, Yoon et al. reported the gaps in patella eversion demonstrated smaller gaps both in knee extension and flexion position compared to the gaps of patella reduction position. The amount of decreased gaps was more definite in knee flexion position. Therefore, the intraoperative patellar positioning has influence on the measurement of the joint gap. Keeping the patella in reduced position is important during gap balancing [18].

16.3.1 Medial Release

As for varus deformity, release is mostly conducted in tibia, and if the ligament tissue is released in the form of sleeve, it is scarred into a thick connective tissue after the surgery, which poses little difficulty to its function, whereas transverse incision poses a lot of difficulty in function and should not be performed. Medial release is first conducted on medial semimembranosus tendon, at last as argued by some operators, or not at all or partially by others. Most of the operators gradually release superficial medial collateral ligament (MCL) until lower extremity alignment returns. Clayton recommended the superficial MCL release to be conducted up to 5–6 cm before semimembranosus [19]. However, Insall et al. argued that it must be conducted in 7–8 cm to fulfill wanted goals [20]. Matsumoto et al. argued that semimembranosus release does not influence clinical outcome but reduces tibial internal rotation and flexion angle in cruciate-retaining total knee arthroplasty [21]. Also, Ahn argued that in severe varus knee, bony resection of proximal medial tibia can be considered as an alternative technique in order to decrease total operation time and to obtain medial-lateral, soft-tissue balance in deep flexion, rather than medial soft-tissue release [22].

Whiteside reported that release of the posterior part of superficial MCL is useful for extension contracture and releasing anterior part of MCL is effective for flexion tightness [23]. Burkart et al. conducted TKA with 12 cadaveric specimens and found that the medial parapatellar arthrotomy and ACL and PCL sectioning did not result in medial or lateral gap length. The release of the anterior fibers of the deep MCL as part of the surgical exposure increased the medial gap [24]. Also, pie crust can be conducted on superficial MCL with multiple pinning or 18 gauge needle, which must be conducted in moderate or intermediate tightness. Meneghini et al. argued pie crust method should be carefully performed, and with wrong technique, stroma of collateral ligament may rupture in joint line, which is worse than avulsion of distal part [25].

If medial gap loosening occurs in flexion after medial release, surgeon should inspect if there are external rotation of femoral component, varus resection of tibia, and whole damage of medial MCL component. If there is no specific abnormality in such inspection, small medial gap laxity in flexion is acceptable. Insall argued that large medial gap is not clinically big problem and takes time for scarring adhesion [20]. Alternative for medial release is “shift and resect” by Dixon which places a small trial in lateral side and makes more posteromedial marginal bone resection. This procedure can have same effect of MCL release [26].

16.3.2 Lateral Release

Valgus deformity of knee joint is not as common as varus deformity. Therefore, operators are not used to the surgery, and it is very difficult to release complex contracture of lateral soft tissue and ligament. Unless it is valgus deformity, general TKA rarely requires lateral release, but if insertion of thick PE is necessary due to excessive medial looseness, lateral side must be released to balance the knee. In such case, lateral collateral ligament or popliteus tendon may be released, and it is important that how much and how release is conducted. Kesman et al. evaluated influence of popliteus tendon resection during posterior stabilized TKA surgery and found that resection of popliteus tendon does not have great influence in static balance during flexion and extension [27]. However, in such cases, ML ligament release is too excessive, and it may require constrained prosthetics, which requires delicate attention.

16.3.3 Intraoperative Mediolateral Gap Check Device

Although advances in navigation system in TKA have improved the incidence of alignment outliers, spatial distance measurements do not quantify soft-tissue stability or degrees of ligament tension. Recently, the development of integrated microelectronics and sensors into the knee trials (device that shows the force applied on mediolateral and anteroposterior part of the insert with attached sensor in digital number) during surgery allows surgeons to evaluate and act on real-time data regarding implant position, rotation, alignment, and soft-tissue balance through a full range of motion (Fig. 16.3). Gustke argued that ensuring soft-tissue balance by using intraoperative sensors during TKR may improve satisfaction [27]. Meneghini et al. measured intraoperative ligament balance with force-sensing implant trials and studied if an optimal “target” balance exists. Intraoperative force sensing has potential in providing real-time objective data to optimize TKA outcomes. These data support some early outcomes may improve by balancing TKAs within 60 lb. mediolateral force difference [28]. Jacob et al. previously reported that symmetrical medial and lateral compressive forces did not improve patient satisfaction, but recreating greater forces in the medial compartment much like that of the native knee may yield improved patient-reported outcomes and increased patient satisfaction. The current results further suggest that recreating greater medial compartment forces may have the greatest effect on more demanding activities [29].