Limb length discrepancy after total knee arthroplasty: A systematic review and meta-analysis

Table 1 Methodological quality assessment of eligible studies using Newcastle–Ottawa scale

Ref.	Selection				Comparability	Outcome
	Representativeness of exposed cohort	Selection of nonexposed cohort	Ascertainment of exposure	Demonstration that outcome of interest was not present at start of study	Adjust for the most important risk factors	Adjust for other risk factors	Assessment of outcome	Follow-up length	Loss to follow-up rate	Total quality score
	Postoperative limb length	Preoperative limb length	TKA	Limb lengthening/LLD	Age, sex, BMI	Varus/valgus deformity, KL grade etc.	Limb length change	Any postoperative period	< 20%
Vaidya et al[11], 2010	+	+	+	+	-	-	+	+	+	7 (moderate risk)
Lang et al[12], 2012	+	+	+	+	+	+	+	+	+	9 (low risk)
Chang et al[13], 2013	+	+	+	+	+	+	+	+	+	9 (low risk)
Tipton et al[14], 2015	+	+	+	+	+	+	+	+	+	9 (low risk)
Kim et al[4], 2015	+	+	+	-	+	+	-	+	+	7 (moderate risk)
Goldstein et al[15], 2016	+	+	+	+	+	+	-	+	+	8 (moderate risk)
Chinnappa et al[16], 2017	+	+	+	+	+	+	+	+	+	9 (low risk)
Hinarejos et al[17], 2020	+	+	+	+	+	+	+	+	+	9 (low risk)

TKA: Total knee arthroplasty; LLD: Limb length discrepancy; BMI: Body mass index.

Table 2 Details of the patients, intervention and follow up duration as mentioned in the studies

Ref.	Inclusion/exclusion criteria	No of knees (UL, BL)	Study design	Age in years ± SD (range)	Sex (M:F)	BMI (Kg/m2)	Intervention (TKA)	Follow up
Vaidya et al[11], 2010 (level IV)	BL OA knee with varus deformity, operated for unilateral or bilateral TKA with minimum 6 mo follow up (n = 54 pts)	30 UL	Cohort retrospective	64 (48-80)	7:23	-	Mid-vastus approach; PFC sigma RP-F Highflex (56), PFC Sigma RP (26), IB II Zimmer (2); Patella replaced	Minimum 6 mo
		30 BL (six pts underwent stage wise TKA, included in both groups)	Cohort retrospective	65.8 (54-83)	6:24	-		Minimum 6 mo
Lang et al[12], 2012 (level III)	BL OA knee (both varus and valgus) without significant extraarticular deformity (n = 102 pts)	102 (54 UL, 47 BL)	Cohort retrospective	70.3 ± 9.9	35:67	30.0 ± 6.4	Medial parapatellar approach, principles of flexion/extension gap balancing85 CR and 17 PS	6 wk
Chang et al[13], 2013 (level III)	Inclusion: TKA for primary OA knee with one year follow up. Exclusion: Pts with previous surgery on the ipsilateral limb, spine surgery, neurological disorders, cancer, death due to diseases unrelated to TKA, periprosthetic infection, or another condition capable of affecting the result of this study, such as depression, dementia, or problems of the contralateral knee were excluded (n = 466 pts)	761 knees (171 UL, 295 BL, 466 patients)	Cohort Retrospective study (prospectively collected data)	67.9 ± 5.9 (49–84)	26:440	27.1 ± 3.4	Medial parapatellar approach, patella replaced	1 yr
Tipton et al[14], 2015 (level III)	Inclusion: Primary TKA with availability of both preoperative and postoperative standing full-length radiographs for measurement. Exclusion: Patients with gross bony deformities or poor quality radiographs were excluded (n = 137)	137 UL	Cross sectional Prospective study	68 ± 10	40:82	30 ± 5.0	Medial parapatellar approach, minimal bone resection with thinnest poly-insert	Postoperative setting
Kim et al[4], 20151 (level IV)	Inclusion: Primary computer-assisted TKA in OA knee with varus deformity. Exclusion: Varus > 20°, hip pathology, osteotomy in the affected limb, severe bony defects, severe osteoporosis, flexion contracture > 30°, BMI > 30 kg/m2, and spine deformity with pelvic tilt	148 (≤ 15 mm LLD in 81 knees, 55 pts; > 15 mm LLD in 67 knees, 52 pts)	Cohort retrospective	≤ 15 mm: 69.1 ± 6.7; > 15 mm: 70.1 ± 8.4	15:133	≤ 15 mm: 26.3 ± 3.2; > 15 mm: 27.1 ± 3.6	Mid-vastus approach, Orthopilot navigation system. PS implant. No patella resurfacing	Minimum 2 yr
Goldstein et al[15], 2016 (level III)	Inclusion: Primary TKA for unilateral osteoarthritis between 18-90 yr of age. Exclusion: Pts with allergy or intolerance to the study materials, previous surgeries on the ipsilateral or contralateral joints or limbs likely to affect the outcome, substance abuse or dependence within the past 6 mo (n = 71)	71 UL	Cross sectional prospective study	65 ± 8.4 (47-89)	27:44	35.1 ± 9.9 (20.2-74.8)	Medial parapatellar or midvastus approach	1 yr
Chinnappa et al[16], 2017 (level II)	Inclusion: Primary unilateral TKA without extraarticular deformity (n = 91). Exclusion: Patients with known leg length inequality due to other causes (radiographic leg lengthening post THA > 5 mm and longstanding leg length inequality > 5 yr requiring orthotics) were excluded.	91 UL	Cohort. Prospective study	70.2 ± 8.9 (50-89)	34:57	29.4 ± 5.0 (17.5–48.6)	Medial parapatellar approach, aim to restore neutral HKA axis. PS implant. Bone resection using Jig or computer navigation	Radiographic measurement on second postoperative day, functional outcome at 6 mo
Hinarejos et al[17], 2020 (level II)	Inclusion: Unilateral primary TKA. Exclusion: Pts with previous fractures of the lower limbs, patients with surgeries or diseases affecting any of the hips or ankles, preoperative or postoperative flexion contracture > 5°, poor quality radiographs, patients without postoperative KSS evaluation (n = 460)	460 UL	Cohort. Prospective study	71 ± 8.4	128:332	31.3 ± 4.9	Medial parapatellar approach; intramedullary guide for femur and extramedullary jig for tibia, minimal bone resection with thinnest insert. CR in 30.4%, PS in 69.6%. Patella replaced	At 6 mo, radiographic evaluation; at 1 yr, functional evaluation

¹The study by Kim et al[4], 2015 divided the study group into LLD ≤ 15 mm vs > 15 mm and then compared.

OA: Osteoarthritis; UL: Unilateral; BL: Bilateral; M: Male; F: Female; BMI: Body mass index; LLD: Limb length discrepancy; CR: Cruciate retaining; PS: Posterior stabilized; KSS: Knee society score; TKA: Total knee arthroplasty; HKA: Hip—knee—ankle angle.

Table 3 Limb lengthening/limb length discrepancy after total knee arthroplasty surgery

Ref.	Deformity (degree)			Pre-op LLD (mm)	Postop LLD (mm)	% of patients with limb lengthening/LLD	Limb lengthening (mm)	% of patients with perceived postop LLD	Factor affecting radiographic LLD/remarks
	Preop (o)	Postop (o)	Change in alignment (o)
Vaidya et al[11], 2010	-	-		-	15.3 ± 2.88	83.3 (≥ 10 mm in all)		8 (26.7)	LLD is more common after unilateral TKA than bilateral. LLD of ≥ 2 cm is perceived by patient after unilateral TKA. LLD affects the functional outcome after UL TKA in BL OA knee with varus deformity
	-	-		-	5 ± 2.01	46.66 (≥ 10 mm in all)		0
Lang et al[12], 2012	2.5	1	1.5	-	2 (95%CI: 0.5-3.5)	83.3%	6.3 ± 6.85 (range -11-24)	-	Limb lengthening is frequent after TKA and is almost similar to that of nonoperative limb. Limb lengthening had no relationship with age (P = 0.864), sex (P = 0.514), BMI (P = 0.548), or constraint type (P = 0.849), contralateral OA knee severity. LLD in bilateral TKA is minimal but it is significantly different in unilateral TKA
Chang et al[13], 2013	11.9 ± 5.5º (37o to -9º)	1.5 ± 2.7 (11o to -6o)	10.4	6 ± 5	5 ± 4	43.9% limb lengthening by ≥ 10 mm, 3.4% limb shortening of ≥ 10 mm	9 ± 1.1	-	Greater LL increase was correlated with a greater preoperative HKA angle and smaller BMI. Preoperative flexion contracture, postoperative flexion contracture and postoperative HKA have no correlation to LL. Limb length, height, and weight increased, BMI remained unchanged, and LLD decreased 1 year after TKA. The bilateral group had a greater height increase and lower rate of LLD
Tipton et al[14], 2015	4.16	2.76	1.40	-	-	59.1%	4.28 ± 1.11, 59% reported increase in limb length by 4.38 mm		There was no correlation BMI with limb length. Limb lengthening after TKA does not frequently occur to a statistically significant extent, regardless of preoperative joint state
Goldstein et al[15], 2016	-	-	-	-	-	-	-	10%	Perceived LLD is common in patients undergoing TKA and it decreases after surgery. About 10% of patients perceive a LLD after surgery and it usually resolves with time. Age, BMI, Preoperative and postoperative mechanical axis and preoperative perceived LLD has no correlation with postoperative perceived LLD
Chinnappa et al[16], 2017	-3.1	0.8	3.9	-3.0 ± 8.0	0.4 ± 10	77% (≥ 10 mm in 11%)	3.5 ± 8.4 (77% lengthened: Mean 6.7 ± 4.9 mm; 23% shortened: Mean -7.4 ± 8.5)	14%	Radiographic LLD is uncommon after TKA. It has no correlation with age, sex, BMI, polyethylene insert thickness, pre-operative FFD, post-operative FFD, contralateral knee OA, or arthroplasty, severity of pre-operative angular deformity or degree of angular correction. Post-operative radiographic LLD is associated with increased preoperative LLD (P < 0.001). Perceived post-operative LLD was associated with female gender (P = 0.02), decreased satisfaction (18% vs 84%, P < 0.001) and poorer functional score
Hinarejos et al[17], 2020	5.5 ± 7.7	3.7 ± 3.8	1.8	-1.1 ± 6.4	0.8 ± 6.1	60% (≥ 10 mm in 8.26%)	1.9 ± 8.84		Increased LLD has no correlation with age, gender, BMI, HKA angles or with preoperative knee function. However HKA angle changes correlate with LLD. Significant LLD is not frequent after TKA, but the functional results of the surgery can be suboptimal when it is present

Limb length measurement: Vaidya et al[11], 2010-clinical method of measurement using measuring tape was used for limb length measurement in supine position; remaining. OA: Osteoarthritis; BMI: Body mass index; LLD: Limb length discrepancy; TKA: Total knee arthroplasty; HKA: Hip—knee—ankle angle.

Table 4 Factors affecting limb length variation/limb length discrepancy in total knee arthroplasty

Ref.	Type of deformity
	Varus					Valgus
	No of knees	Preop varus (o)	Postop varus (o)	Change in angle	Average lengthening	No of knees	Preop varus (o)	Postop varus (o)		Change in angle	Average lengthening
Lang et al[12], 2012	66	8.7 ± 4.6	2.1± 2.5	-6.6	5.2 ± 5.8 (S)	36	-8.9 ± 5.9	-1.1 ± 3.3		-7.8	8.4 ± 8.2 (S)
Tipton et al[14], 2015	87	9.34 ± 4.66	4.86 ± 3.03	-4.99 (4.77)	3.77 ± 11.1 (S)	45	-6.67 ± 5.79	-0.468 ± 3.57		-6.08 ± 5.72	5.56 ± 11.3 (S)
	Severity of deformity
	-10 to 10 degree		< -10 (valgus)		> 10 (varus)
	No of knees	Limb length change	No of knees	Limb length change	No of knees	Limb length change
Lang et al[12], 2012	65	4.7 ± 6.4 (S)	12	12 ± 8.6 (S)	25	7.9 ± 5.2 (S)
Tipton et al[14], 2015	93	1.64 ± 10.3 (NS)	9	15.1 ± 10 (NS)	35	8.51 ± 10.7 (NS)
	Unilateral or bilateral TKA
	Unilateral TKA		Bilateral TKA
	No of knees	LLD	No of knees	LLD
Vaidya et al[11], 2010	30	15.3 ± 2.88	30	5 ± 2.01 (S)
Lang et al[12], 2012	54	3.0 (95%CI: 0.5-5.4, NS)	47	0.9 (95%CI: −0.9-2.7, NS)
Chang et al[13], 2013	171	6 ± 4	295	5 ± 4 (S)
	Severity of OA in contralateral nonoperative limb/ipsilateral limb in preoperative period
	KL 1, 2			LLD (mm)		No of knees in KL 3, 4			LLD (mm)
Lang et al[12], 2012	Contralateral knee OA status (n = 26)			2 ± 5		Contralateral limb status (n = 28)			3.9 ± 11.5 (NS)
Tipton et al[14], 2015	Ipsilateral preop knee OA status			-2.00 ± 8.87 (only limb lengthening)		Ipsilateral preop knee OA status			0.594 ± 1.11 (NS)

S: Significant P < 0.05, NS: Non-significant P > 0.05; OA: Osteoarthritis; LLD: Limb length discrepancy; TKA: Total knee arthroplasty.

Table 5 Correlation of limb length discrepancy to functional outcome

Ref.	Functional score	Functional outcome	LLD vs functional outcome	Perceived LLD	Remarks
Vaidya et al[11], 2010	Knee society clinical rating system	Mean score in UL group was 73 ± 16.79 (95%CI: 66.73-79.27 (range 45-100)	No LLD (5): Functional score 85; LLD 10 mm (5): functional score 83; LLD 20 mm (19): Functional score 68.16; LLD 30 mm (1): Functional score 55; < 10 mm (21): 82.1429 ± 9.439; ≥ 10 mm (39): 73.9744 ± 5.261	26.66% (8) pts perceived LLD; no LLD: Not perceived; LLD 10 mm: Not perceived; LLD 20 mm: 7 patients; LLD 30 mm: One patient	The functional outcome after UL TKA in BL OA knee with varus deformity is inferior to BL TKA
	Knee society clinical rating system	Mean score in BL group was 80.67 ± 21.2 (95%CI: 72.75 -88.58, range 0-100).	No LLD (16): Functional score 81.25; LLD 10 mm (13): Functional score 80; LLD 20 mm (1): Functional score 80	No one perceived LLD
Kim et al[4], 2015	KSS function score		LLD > 15 mm: KSS function score 88.2 ± 7.0; LLD ≤ 15 mm: KSS function score 80.1 ± 14.7 (S); no difference in ROM, HSS, KSS knee score and WOMAC	Not evaluated	Patients with LLD of > 15 mm had significantly inferior outcome than LLD < 15 mm. Preop LLD has high risk of postop LLD. Patients with unilateral TKA have higher chances of postoperative LLD
Chinnappa et al[16], 2017	WOMAC; KSS knee; KSS; function 6 mo		LLD < 10 mm: 89% pts.; LLD ≥ 10 mm: 11% pts. a: 37.1 ± 16 in ≥ 10 mm LLD vs 30.8 ± 21.2 with < 10 mm LLD (NS); b: 37 ± 20.8 in ≥ 10 mm LLD vs 29.2 ± 35.2 with < 10 mm LLD (NS); c: 29.4 ± 21.2 in ≥ 10 mm LLD vs 23.6 ± 27.7 with < 10 mm LLD (NS)	Preoperative LLD: 16% pts. Postoperative LLD: 21% pts. a: 13.1 ± 22.6 in ≥ 10 mm LLD vs 35.5 ± 18.8 with < 10 mm LLD (S); b: 16.2 ± 26.2 in ≥ 10 mm LLD vs 31.0 ± 34.1 with < 10 mm LLD (NS); c: 15.3 ± 28.9 vs 26.1 ±27.1 (NS)	Significant radiological LLD (≥ 10 mm) after TKA is uncommon (11%) and doesn’t correlate to perceived LLD. Perceived LLD is associated with decreased satisfaction and function
Hinarejos et al[17], 2020	Function KSS	Mean preop score of 51.3 ± 13.5 improved to 80.5 ± 15.1 at 12 mo (P < 0.0001)	LLD < 10 mm (422, 91.7%): Functional score 82.3 (14.6). LLD ≥ 10 mm (38, 8.3%): Functional score 76.7 (14.0)	Not evaluated	Patients with LLD of > 10 mm had significantly worse outcome

S: Significant P < 0.05; NS: Non-significant P > 0.05; KSS: Knee society score; HSS: Hospital for special surgery score; WOMAC: Western Ontario and McMaster Universities scores; LLD: Limb length discrepancy; TKA: Total knee arthroplasty.