Short-term outcome of 1,465 computer-navigated primary total knee replacements 2005–2008

Figures & data

Figure 1. Selection of cases. NAR: Norwegian Arthroplasty Register; TKR: total knee replacement; CAS: computer-assisted surgery (abbreviation for computer-navigated knee replacements in the article), CON: conventionally operated knee replacement, using either intra-medullary or extra-medullary alignment rods.

Table 1. Demographic data of primary total knee replacements without patella component (computer navigated (CAS) or conventionally operated (CON)) reported to the Norwegian Arthroplasty register, 2005–2008

	CAS	CON	p-value
Number	1,465	8,214
Men %	39	33	< 0.001
Age, years	68.8	69.8	0.001
95% CI	68.3–69.3	69.5–70.0	0.001
Right knee, %	56	55	0.3
MIS ^a , % (n)	0 (7)	0 (21)	< 0.001
ASA category ^b , % (n)			0.03
1	19 (272)	22 (1,766)
2	62 (907)	57 (4,706)
3	18 (266)	20 (1,630)
4	0 (2)	0 (14)
missing	1 (18)	1 (98)
Diagnosis preoperatively, %
Primary gonarthritis	90	89	0.1
Other	10	11
Fixation method, % (n)			< 0.001
Cemented	75 (1,087)	84 (6,794)
Uncemented	19 (278)	1 (111)
Hybrid (uncemented femur)	6 (82)	15 (1,203)
Prosthesis brand, % (n)			< 0.001
AGC	5 (80)	13 (1,072)
Duracon	11 (168)	5 (443)
e.motion	21 (300)	0 (7)
LCS complete	39 (570)	35 (2,834)
Profix	24 (347)	47 (3,858)
Prosthesis design, % (n)
Fixed bearing	41 (595)	65 (5,373)	< 0.001
Mobile bearing	59 (870)	35 (2,841)	< 0.001
Stabilized ^c	2 (25)	2 (174)	0.2
Previous operations of the knee, %	37	27	< 0.001
Osteosynthesis affecting the knee joint	3	2	0.02
Osteotomy	5	4	0.3
Synovectomy	2	2	0.9
Other	30	21	< 0.001
Intact ACL ^d preoperatively, %	71	81	< 0.001

^a MIS: minimally invasive surgery.

^b ASA category: American Society of Anesthesiologists physical status classification system.

^c Polyethylene insert posteriorly stabilized or other stabilization.

^d ACL: anterior cruciate ligament.

Table 2. Kaplan-Meier survivorship (KM) and adjusted Cox regression relative risk for conventionally operated (CON) and computer-navigated (CAS) primary total knee replacements without patella resurfacing reported to the Norwegian Arthroplasty Register, 2005–2008

	Revised/ total (%)	MF ^a (years)	1 year At risk	1 year KM survival (95% CI)	2 years At risk	2 years KM survival (95% CI)	2005–2008 Cox-adjusted ^b relative risk (95% CI)
CON	149/8,214 (1.8%)	1.8	5,776	98.8 (98.6–99.0)	3,520	97.9 (97.5–98.3)	1
CAS	32/1,465 (2.2%)	1.4	757	98.5 (97.7–99.3)	400	96.4 (95.0–97.8)	1.7 (1.1–2.5) ^c

^a MF: mean follow-up (reversed KM).

^b Adjusted for sex, age, prosthesis brand, preoperative diagnosis, previous knee surgery, fixation method, and ASA category.

^c P-value = 0.019

Figure 2. Cox regression survival curves of computer-navigated (CAS) and conventionally operated (CON) primary total knee replacements, without patella resurfacing, reported to the Norwegian Arthroplasty Register 2005–2008.

Figure 3. A. Cox regression survival curves of conventionally operated knee replacements (CON) sorted into various prosthesis brands, as reported to the Norwegian Arthoplasty Register 2005–2008. B. Cox regression survival curves of computer-navigated knee replacements (CAS) sorted into various prosthesis brands.

Table 3. Intraoperative complications occurring more frequently than 1 in 1,000

	Instrument failure	Fracture of the tibia	Cement failure	Anesthesia failure	Torniquet failure	Patella tendon rupture/avulsion or ligamentous/tendinous injury
CON	10	15	6	0	8	21
CAS	5	4	3	3	3	4
p-value ^a	0.1	0.5	0.1	0.003	0.2	0.8

^a By Fisher's exact test.

Table 4. Total knee replacements reported to the Norwegian Arthroplasty Register, 2005–2008: causes of revision and Cox relative risk (RR) with 95% CI. Computer-navigated TKRs (CAS) and conventionally operated TKRs (CON) are compared. (There may have been more than one cause of revision reported in each case)

	A	B	C	D	E	F	G	H	I	J	K	L
CON, n	8	22	3	4	22	11	36	6	63	6	19	149
CAS, n	0	8	1	0	2	1	13	1	13	0	1	32
RR CAS vs CON	–	2.1	2.4	–	0.6	0.7	1.7	0.9	1.3	–	0.3
(95%CI)		0.9–4.9	0.2–25		0.1–2.4	0.1–5.6	0.9–3.3	0.1–7.7	0.7–2.5		0.04–2.2

A Loose femoral component

B Loose tibial component

C Dislocated patella

D Dislocation (not patella)

E Instability

F Malalignment

G Deep infection

H Fracture (affecting implant)

I Pain

J Defect polyethylene insert

K Other

L Total no. revised