Validation of 14,500 operated knees registered in the Danish Knee Ligament Reconstruction Register: registration completeness and validity of key variables

Figures & data

Table 1 Patient characteristics

Patient characteristics	Type of register
	Both DNRP and DKRR, n (%) n = 12,963	DNRP only, n (%) n = 3550	DKRR only, n (%) n = 1537
Sex
Male	7783 (60.0)	2208 (62.2)	937 (61.0)
Female	5180 (40.0)	1342 (37.8)	600 (39.0)
Mean age at surgery	29.7 (95% CI: 29.5–29.9)	31.0 (95% CI: 30.6–31.3)	31.9 (95% CI: 31.4–32.5)
Age at surgery (years)
≤20	3449 (26.6)	773 (21.8)	299 (19.5)
>20	9514 (73.4)	2777 (78.2)	1238 (80.5)

Abbreviations: DNRP, Danish National Registry of Patients; DKRR, Danish Knee Ligament Reconstruction Register; n, number; CI, confidence interval.

Figure 1 Development of data completeness in the DKRR.

Abbreviation: DKRR, Danish Knee Ligament Reconstruction Register.

Table 2 Completeness of registration of ACL reconstruction surgery in the DKRR compared with the DNRP

	Type of register			Total (n)	Degree of completeness % (95% CI)
	Both DNRP and DKRR n (%)	DNRP only n (%)	DKRR only n (%)
2005–2011	12,963 (71.8)	3550 (19.7)	1537 (8.5)	18,050	78.5 (77.9–79.1)
≤20 years	3449 (76.3)	773 (17.0)	299 (6.6)	4521	81.8 (80.6–82.9)
>20 years	9514 (70.3)	2777 (20.5)	1238 (9.2)	13,529	77.4 (76.7–78.1)
Male	7783 (71.3)	2208 (20.2)	937 (8.6)	10,928	77.9 (77.1–78.7)
Female	5180 (72.7)	1342 (18.8)	600 (8.5)	7122	79.4 (78.4–80.4)
Small volumea	1317 (56.0)	726 (30.8)	311 (13.2)	2354	64.5 (62.3–66.5)
Large volumea	11,646 (75.1)	2628 (17.0)	1226 (7.9)	15,500	81.6 (80.9–82.2)
2005	690 (52.2)	455 (34.5)	176 (13.3)	1321	60.3 (57.4–63.1)
2006	1870 (65.6)	758 (26.6)	224 (7.8)	2852	71.2 (69.4–72.9)
2007	1828 (67.5)	660 (24.4)	219 (8.1)	2707	73.5 (71.7–75.2)
2008	1737 (70.7)	480 (19.9)	231 (9.4)	2458	78.0 (76.2–79.7)
2009	2335 (77.3)	407 (13.5)	278 (9.2)	3020	85.2 (83.8–86.5)
2010	2323 (77.6)	433 (14.5)	238 (7.9)	2994	84.3 (82.9–85.7)
2011	2180 (80.8)	347 (12.9)	171 (6.3)	2698	86.3 (84.9–87.7)

Notes: Results were stratified according to patient sex, age, and small-volume versus large-volume hospitals.

a 196 ACL-reconstructed knees that could not be placed in either the small-volume or the large-volume group because of imprecise definition in the DNRP.

Abbreviations: ACL, anterior cruciate ligament; DKRR, Danish Knee Reconstruction Register; DNRP, Danish National Registry of Patients; n, number; CI, confidence interval.

Table 3 Validity of key variables registered in DKRR

	DKRR database	Medical record		Missing medical record	PPV% (95% CI)
		Yes	No
Cartilage lesion	Yes	29	5	0	29/34 = 85 (69–95)
	No	27	127	12
	Missing DKRR	13	26	1
Treated meniscal lesionsa	Yes	103	4	0	103/107 = 96 (90–99)
	No	26	107	0
Sport as activity reason for the ACL rupture	Yes	172	29	1	172/201 = 86 (80–90)
	No	4	33	0
	Missing DKRR	0	1	0
Diagnosis of ACL lesion	Yes	240	0		240/240 = 100
	No	0	0
Hamstring as graft choiceb	Yes	208	0	2	208/208 = 100
	No	0	24	0
	Missing DKRR	4	1	1
Transtibial placement of femoral canal	Yes	136	6	60	136/142 = 96 (91–98)
	No	3	18	16
	Missing DKRR	1	0	0
One femoral canal (versus two)	Yes	237	0	2	237/237 = 100
	No	0	0	0
	Missing DKRR	1	0	0
OP date	Identical	238	0	1	238/239 = 99 (93–100)
	Not identical	0	1
Method for fixation of graft in femur	Identical	217		7	217/233 = 93 (89–96)c
Method for fixation of graft in tibia	Identical	220		6	220/234 = 94 (90–97)c

Notes: Medical records were used as a reference standard, and 240 medical records were used. “Identical” indicates that the registration in the DKRR is identical to the registration in the medical records.

a The registration of this variable in DKRR is to choose a treatment of the meniscal lesion. Hence, if no registration is made in this variable it can be etiher: no treatment or a missing value

b comparing if hamstring or bone–patellar tendon–bone graft is used. Other graft choices were deleted because they account for less than 2%

c About 20 different modes of fixation are possible in this variable. Therefore, calculation of completeness was made by inputing the number of variables registered identical in the DKRR and in the medical records into the numerator, and dividing them by all the cases registered in the denominator.

Abbreviations: DKRR, Danish Knee Ligament Reconstruction Register; PPV, positive predictive value; CI, confidence interval; ACL, anterior cruciate ligament; OP, operation.

Table 4 Results from questionnaires on KOOS and Tegner scores

Previously answered subjective measures	N	Pain mean (SD)	Symptom mean (SD)	Activity of daily living mean (SD)	Sport mean (SD)	Qol mean (SD)	Tegner mean (SD)
Yes (responders)	62	83.1 (15.0)	60.4 (13.8)	88.0 (15.7)	64.5 (26.9)	64.5 (25.4)	4.87 (2.0)
No (nonresponders)	39	78.5 (19.2)	59.8 (12.1)	83.7 (19.7)	56.9 (26.8)	59.3 (24.5)	4.56 (1.9)
P-value		0.09	0.38	0.12	0.97	0.82	0.72

Notes: Mean value of the different subjective scores in the group of patients who previously recorded subjective scores (responders) compared with the group of patients who did not previously record subjective scores (nonresponders).

Abbreviations: KOOS, Knee injury and Osteoarthritis Outcome Score; N, number; SD, standard deviation; Qol, quality of life.

Table 5 Patient characteristics from the Danish Knee Reconstruction Registry with (responders) or without (nonresponders) subjective scores registered 1 year postoperatively

Patient characteristics	Subjective scores registered 1 year after operation
	Yes, n (%)	No, n (%)
Sex
Male	2240 (58.1)	6704 (62.9)
Mean age at time of surgery (years)	30.5 (95% CI: 30.1–30.8)	29.7 (95% CI: 29.5–29.9)
Age at time of surgery (years)
≤20	965 (25.1)	2928 (27.5)
ACL revision
Yes	144 (3.7)	255 (2.4)
Meniscal treatment
Yes	1444 (37.5)	4227 (39.6)
Cartilage damage
Yes	713 (18.5)	2369 (22.2)
Prior knee surgery
Yes	1086 (28.2)	2935 (27.6)
Sport activity leading to tear
Yes	3328 (86.4)	8761 (82.2)
Graft choice (hamstring)
Yes	2974 (77.2)	8767 (82.3)

Abbreviations: n, number; ACL, anterior cruciate ligament; CI, confidence interval.