Study on the learning curve during the transition from direct lateral to direct anterior approach in total hip arthroplasty : a consecutive one hundred and twenty-seven case series

doi:10.21203/rs.3.rs-1751513/v1

Background: Direct anterior approach (DAA) for primary hip arthroplasty has received increasing attention recently. However, there have been no reports focused on the learning curve when transitioning from direct lateral approach(DLA) to DAA. This study evaluates a single surgeon’s learning curve by examining Procedure Time (PT), Operation Preparation Time (OPT), Operating Room Time(ORT) and other data.

Methods: From 2019 to 2021, a single surgeon’s first 100 cases with DAA and 27 cases with DLA between the learning cure were reviewed. PT, OPT, ORT and other data were analyzed.

Results: Compared with DLA, PT, OPT and ORT had a sharp rise in the first 10 cases. There was no statistical significance in PT after 20 cases, ORT after 30 cases, and OPT after 50 cases. The difference of PT and ORT between group 1(DLA) and group 2(DAA, 1-51 cases), group 2 and group 3(DAA, 51-100 cases) were statistically significant. OPT of Group 1 was the shortest, increased significantly in group 2, gradually decreased in group 3. There were significant differences in blood loss between group 1 and group 3, between group 2 and group 3. 4 complications in total, 1 case in group 1, 3 cases in group 2. There were no significant differences in blood transfusion, length of stay and complication rate.

Conclusions: When transitioning from DLA to DAA, an experienced surgeon may be low efficient, with longer PT, OPT and ORT. Great changes appeared after DAA 50 cases, complications and blood loss could be controlled within the safe range.

total hip arthroplasty

direct anterior approach

direct lateral approach

learning curve

complication

Hailed as a surgical milestone in the 20th century, total hip arthroplasty (THA) has become the preferred treatment for a wide range of hip disorders. There are three main approaches for THA: posterolateral approach, direct lateral approach (modified Hardinge), and direct anterior approach (DAA)^[1]. Among them, DAA has a longest history since it was proposed in 1881. However, it was not until 2009 when Rachbauer reported his experience of total hip arthroplasty via DAA on a common operating table that DAA gradually drew the attention of more and more joint reconstruction surgeons^[2]. More than 30% of American surgeons are currently performing or attempting DAA, and the DAA currently accounts for about 10% of all THAs^[3,4].

DAA is the true minimally invasive approach for THA which utilizes both an intermuscular and internervous plane, leaving all muscular attachments intact. The advantages of this approach also include less blood loss, decreased postoperative pain, shorter hospital length of stay,quicker recovery, and a lower incidence of hip dislocation^[5-9]. Proponents of DAA also believe that the acetabular components are better positioned because of intraoperative fluoroscopy^[10^-13^]. However, a variety of of complications ( injury of the lateral femoral cutaneous nerve, wound infection, and intraoperative fracture) and increased complication incidence have also been reported in the paper. Most of these complications occur in early cases and have a lot to do with the learning curve of technology transition^[14-17].

The learning curve is defined as the number of cases a surgeon requires of a new procedure before outcomes approach a steady state compared with their standard procedure. To our knowledge, there was no published study focusing on the learning curve of a single surgeon's transition from direct lateral approach to DAA. In this study, we will attempt to establish such a learning curve by looking at 127 consecutive DAA hip arthroplasty cases. The focus is on the changes of Procedure Time (PT), Operation Preparation Time (OPT), Operating Room Time (ORT), blood loss, blood transfusion, hospital length of stay and complications.

Population and Data

From February 2019 to June 2021, 127 consecutive cases of primary unilateral THA were performed by a single surgeon in our department from his first DAA case. Before the 50th DAA case was completed, 27 THA cases were performed through DLA (modified Hardinge approach). All cases were screened strictly for surgical indications, and informed consent of patients and their families.

This study was approved by the ethics committee. All data were collected retrospectively and de-identified. The study was a longitudinal analysis and its main purpose was to determine the impact of the cumulative number of consecutive cases on the PT, OPT, ORT and other data. PT was defined as the interval from the beginning of first skin incision to the end of last wound suturing. OPT was defined as the interval from the end of anesthesia to the beginning of first skin incision. ORT was defined as the total interval from the end of anesthesia to the end of surgical suturing, which was also the sum of PT and OPT.

Performing Surgeon

All procedures were performed by an experienced joint reconstruction surgeon specially trained in DAA surgery. A cementless acetabular cup and tapered, cementless stem were used in all cases. All prostheses came from a single manufacturer(Smith & Nephew Inc, Memphis, TN). Before the initiation of the first case, this surgeon performed more than 50 THAs per year, with the experience of approximately 500 THA performed via DLA. Before that, he received a three-months special training, attended cadaver courses and finished 60 THA cases via DAA as an assistant of skilled DAA surgeons in superior institutions. The surgical team had not participated in a THA surgery via DAA before.

Surgical Technique

DAA: The patient was supine on the operating table. An 10-cm skin incision was made to enter into the intermuscular plane between the sartorius muscle and the tensor fascia lata muscle. After incising the articular capsule, the separated anterior capsule was folded outward as a layer of soft tissue acting as a“pad” covering the outer musculature and sutured to the skin at the edge of the incision with silk suture material^[18]. Then the femoral head was removed and the acetabular cup and lining were put in place. If the femur was difficult to elevate, a portion of the short external rotator muscle could be severed. After intraoperative fluoroscopy, femoral prosthesis was implanted into femoral cavity. At last, the anterior capsule was re-sutured closed.

DLA: The access to the joint was gained through a spilt approach of gluteus medius and gluteus minimus. The cup and stem were implanted by using a combination of anatomic landmarks and mechanical guides. At last, the gluteus medius was re-sutured closed.

Statistical analysis

In order to reflect the transition from DLA to DAA in detail, we first defined the 27 THA cases performed after the initial DAA(February 2019) via the DLA as mature surgery. The mean PT, OPT, ORT of DAA cases were analyzed for a longitudinal series in intervals of 10 cases and compared with the corresponding time of DLA cases. 127 cases were divided into three groups: 27 cases via DLA (group 1), 1-50 cases via DAA(group 2), and 51-100 cases via DAA (group 3). There were no differences in age, gender, or body mass index among the three groups. The PT, OPT, ORT, blood loss, blood transfusion, length of stay and complications among the three groups were compared and analyzed. Gender and complications were compared using chi-square test and Fisher’s exact test. Continuous variables were compared using F-test, independent samples t-test and Welch’s t-test. All analyses were performed using IBM SPSS Statistics, version 26(Armonk, NY). A P value less than 0.05 was treated as statistically significant.

The mean PT of DLA was 107.89 minutes (95% confidence interval, 96.72 - 119.06 minutes). Table 1 details the comparison of mean PT and confidence interval(CI) for the two approaches as the number of DAA cases increases. Figure 1 presents a visual trend of mean PT for DAA and mature DLA at a longitudinal series in intervals of 10 cases. As is shown in Figure 1 and Table 1, transitioning to DAA increased PT by 45.52% over the first 10 cases (P< 0.001); increased PT by 16.60% over the 10-20 case interval (P< 0.05). Over the next 20 to 100 case intervals, the PT was roughly equivalent to that of the DLA(P> 0.05).

The mean OPT of DLA was 26.00 minutes (95% CI, 24.67-27.33minutes). Table 2 details the comparison of mean OPT and CI for the two approaches as the number of DAA cases increase. Figure 2 presents a visual trend of mean OPT for DAA and mature DLA at a longitudinal series in intervals of 10 cases. As is shown in Figure 2 and Table 2, transitioning to the DAA increased OPT by 57.69% 45.00%, 26.54%, 33.08% and 21.15% from the first to the fifth interval (P≤0.001). Over the next intervals, the OPT decreased and still longer than that of the DLA(P> 0.05).

The mean ORT of DLA was 133.90 minutes (95% CI, 123.33 - 144.45 minutes). Table 3 details the comparison of mean ORT and CI for the two approaches as the number of DAA cases increases. Figure 3 presents a visual trend of mean ORT for DAA and mature DLA at a longitudinal series in intervals of 10 cases. As is shown in Figure 3 and Table 3, transitioning from the DLA to the DAA increased ORT by 47.87% to 198.00 minutes over the first 10 DAA cases (P< 0.001); increased ORT by 22.11%, 15.68% over the second and the third interval (P< 0.05). Over the next 30 to 100 DAA case intervals, the mean ORT was roughly equivalent to that of the DLA (P> 0.05).

All the 100 DAA cases were followed up for at least 10 months to identify the complications. All the 3 complications occurred in group 2(3.0%), including 1 lateral femoral cutaneous nerve injury, 1 femoral nerve injury, and 1 greater trochanter fracture. There were no infection, dislocation, aseptic loosening and reoperation. 1 complication occurred in 27 DLA cases(3.70%). Significant limb swelling occurred within 1 week after surgery, which was diagnosed as blood loss from lateral circumflex femoral artery after angiography, and improved after immediate interventional surgery.

Table 4 presents the factor and outcome comparison among the three groups. The results showed that patients in the last 50 DAA cases had less estimated blood loss (206.00 vs 274.07ml, P<0.05, 206.00 vs 291.00, P=0.001). The PT, ORT of the group 1 and group 3 were very close. Patients in the first 50 DAA cases had the longest PT and ORT compared with other two groups. The mean OPT of group 1 was the shortest(26.00 minutes), while it was the longest in group 2. The difference of OPT were statistically significant among the three groups. The mean length of stay in group 2 and group 3 decreased by 20.41% and 24.95% compared with group 1, respectively. The differences of length of stay, blood transfusion and complication rate among three groups were not statistically significant.

Many scholars have tried to define the learning curve of DAA technique using various data, including procedure time, implanted position, fluoroscopy time, complication rate^[19–23]. The learning curve has been previously described as 50–100 cases^[10,23−25]. But previous literature has focused on the transition from posterolateral approach to DAA. So we have attempted to add to the literature defining the learning curve of a single surgeon's transition from DLA to DAA by this retrospective study.

The PT changed most obviously in the first and second intervals, and then decreased slowly. The PT over the 90–100 DAA case interval was 10.37% less than the DLA PT, but the difference was not statistically significant. According to Andrea et al, the PT of DAA was significantly shorter than that of the posterior approach after 850 surgeries^[20]. We believe that the PT of DAA will further decrease with the extension of surgical cases.

Because of different surgical techniques and different preoperative preparation steps, OPT is bound to differ. We found that trend of OPT was significantly different from that of PT. First of all, the increase of the first interval is obviously greater than that of PT, reaching 57.69%. Secondly, the decline in increase is slower. Although the mean OPT was gradually approaching with the extension of surgical cases, it was always longer than that of the DLA. We considered that the preoperative preparation for DAA technique was more complicated, requiring simultaneous disinfection on both sides. Standardized skin preparation and draping procedures would take more time. What’s more, in the whole process of surgery, the surgeon can play a good control, the surgeon's proficiency and state are the most important influencing factors of PT. There are a large number of participants in the process of preoperative preparation, and the influencing factors of personnel are larger.

The DAA requires more like special surgical tools, intraoperative fluoroscopy, foldable operating table, and an experienced surgical team. Because DAA technique had never been performed before, the entire team was built from scratch, including surgical technologists, nursing staff, anesthesia staff, and radiology technicians. The learning curve of DAA does not only belong to a single surgeon, but also for the entire surgical team. A nurse is required to fold the operating table for getting better exposure and convenience of prosthesis implantation. The radiology technician is also important. Using intraoperative fluoroscopy enabled us to gain clear anteroposterior radiographs of the pelvis and lateral radiographs of the femur, so as to select a more appropriate neck length of the femoral prosthesis and better femoral off-set to achieve the limb-length equality. It was not until approximately 80 cases were completed before the ORT of DAA was shorter than that of DLA. Fortunately, there were no intraoperatie injuries such as ankle fractures happen in the operating room^{[26, 27]}.

The major complication rate of DAA in the learning curve has been reported to be 1.6–10%^{[10, 29, 30]}. The complication rate was 3%, which is similar to previous reports. The patient with lateral femoral cutaneous nerve injury complained of obvious hypesthesia in the anterolateral aspect of the thigh 6 weeks after surgery. Improvement of symptoms was seen in the seventh month after takeing mecobalamin tablets (0.5mg TID) for 2 months. The patient with femoral nerve injury had difficulty in walking in the outpatient review at the third month. The quadriceps muscle strength assessed by Lovett scale score was 3. It was considered that the injury was caused by excessive pulling of the hook at the superior ramus of the pubis. The patient received drug treatment (mecobalamin tablets ,0.5mg TID) for 2 months and rehabilitation program. The muscle strength returned to normal one year later. The greater trochanter fracture of the femur occurred in a patient with poliomyelitis sequelae. Muscle atrophy, osteoporosis and inadequate exposure of the greater trochanter led to fracture. The patient was fixed with wire strapping intraoperatively and was instructed to delay weight-bearing and ambulation until 4 weeks. Maratt et al reviewed 2147 THA via DAA. Dislocation occurred in 17 cases and the rate was 0.84%^[31]. According to Kong et al, the dislocation rate was 2%(2/100) including the learning curve^[19]. In our study, there was no dislocation case. Firstly, the surgeon was experienced and was aware of protecting the obturator external tendon. Secondly, by using intraoperative fluoroscopy, a more appropriate neck length could be selected. The acetabulum and femoral prosthesis could be placed in a safer position. Thirdly, our surgical technique adopted articular capsule to cover the outer musculature and to protect the tensor fasciae lata muscle carefully. At last, the anterior capsule was re-sutured closed to improve the stability and to reduce the risk of dislocation. Hallert et al reported 2.5% (5/200) early revisions while no case in this study needed revision surgery^[32]. It might be related to the short follow-up time.

For the first 50 DAA cases, 64.94%(50/77) cases were performed via DAA, while 35.06%(27/77) were performed via the original approach due to various factors. The change of surgical approach is not a simple switch from A to B, but requires a long process of adaptation. We believed that a deeper understanding of DAA had been gained after the completion of 50 DAA cases and most hip joint diseases could be solved by DAA technique. There were statistically significant differences in blood loss, PT, OPT and ORT between group 2 and group 3. All the 3 complications occurred in group 2. A steady state came out after 50 DAA cases.

Shorter length of stay has always been an advantage of DAA over posterolateral and DLA ^{[33, 34]}. However, the difference among three groups was not statistically significant. It may be related to the older age of patients in this group, which leads to more underlying diseases, longer time of routine preoperative medical testing, and slower postoperative recovery.

This study is designed for a single experienced joint reconstruction surgeon and may potentially limit the generalizability of the study. Inexperienced surgeons may have a longer period of learning curve, a higher complication rate, longer PT, OPT and ORT. Visiting experienced DAA surgeons, attending cadaver courses, and restudying possible problems after completing several DAA cases can help a lot ^{[20, 28, 29]}. If possible, we recommend continuing medical education for the entire surgical team.

There are limitations to this study. This is a retrospective study. The overall number of cases was small, the follow-up time was not long, and the diseases of THA patients were not further subdivided, which may not accurately present the learning curve confounding variables. The advantage of this study is that it completely presents the learning curve of THA when transitioning from DLA to DAA. By studying PT, OPT, ORT, blood loss, blood transfusion, length of stay and complications, some interesting trends were found. The learning curve is influenced not only by the individual surgeon, but also by the entire surgical team.

When transitioning from DLA to DAA, an experienced surgeon may be low efficient, with longer PT, OPT and ORT. Great changes appeared after DAA 50 cases, complications and blood loss could be controlled within the safe range.

DAA: Direct anterior approach; DLA: Direct lateral approach; PT: Procedure Time; OPT: Operation Preparation Time; ORT: Operating Room Time; THA: Total hip arthroplasty; BMI:body mass index.

Acknowledgements

Not applicable.

Authors’ contributions

JGZ designed the study and performed all the operations, MC, YW, TJ and WGB performed the research, MC and YW analyzed data, MC wrote the paper. The remaining authors contributed to refining the ideas, carrying out additional analyses

and finalizing this paper. All authors read and approved the final manuscript.

Funding

This work was supported by the National Natural Science Foundation of China (Grant no. 82102643), the Natural Science Foundation of Jiangsu province (BK20180001).

The fund provided financial support for patient follow-up and post-operative review, as well as assistance in data collection, statistics and language polishing.

Availability of data and materials

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Ethics approval and consent to participate

I confirm that all methods were performed in accordance with the Declarations of Helsinki. The approval for this study was obtained from the Institutional Review Board committees of the Yixing People’s Hospital people’s hospital. Informed consent of patients and their families was obtained.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

Author details

¹Department of Orthopaedics, Yixing People’s Hospital, Yixing, Jiangsu, China.

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Table 1 Independent Samples t-Test And Welch’s t-Test Comparing PT Of The Direct Lateral Approach And The DAA Technique At Different Cumulative Case Volumes

DAA Case Interval	Mean Difference	Standard Error	T Value	P Value	95% Confidence Interval
DAA Case Interval	Mean Difference	Standard Error	T Value	P Value	Lower Bound	Upper Bound
0-10	-49.11	10.41	-4.717	0.000	-70.25	-27.98
11-20	-17.91	6.77	-2.646	0.012	-31.68	-4.14
21-30	-13.21	9.86	-1.339	0.189	-33.24	6.81
31-40	-1.61	10.27	-0.157	0.876	-22.47	19.25
41-50	-0.01	9.89	-0.001	0.999	-20.08	20.06
51-60	-6.26	9.98	-0.627	0.534	-26.52	14.00
61-70	-4.01	10.17	-0.395	0.696	-24.65	16.63
71-80	0.29	7.17	0.040	0.968	-14.34	14.92
81-90	0.99	9.74	0.102	0.920	-18.77	20.75
91-100	11.19	9.77	1.146	0.260	-8.64	31.01
PT, procedure time; DAA, direct anterior approach P<0.05, in bold

Table 2 Independent Samples t-Test And Welch’s t-Test Comparing OPT Of The Direct Lateral Approach And The DAA Technique At Different Cumulative Case Volumes

DAA Case Interval	Mean Difference	Standard Error	T Value	P Value	95% Confidence Interval
DAA Case Interval	Mean Difference	Standard Error	T Value	P Value	Lower Bound	Upper Bound
0-10	-15.00	1.82	-8.224	0.000	-18.99	-11.01
11-20	-11.7	1.34	-8.736	0.000	-14.42	-8.98
21-30	-6.90	1.33	-5.193	0.000	-9.60	-4.20
31-40	-8.60	1.36	-6.324	0.000	-11.36	-5.84
41-50	-5.50	1.48	-3.726	0.001	-8.50	-2.50
51-60	-5.35	2.74	-1.953	0.079	-11.45	0.75
61-70	-1.10	1.34	-0.822	0.416	-3.82	1.62
71-80	-3.90	2.33	-1.674	0.123	-9.05	1.25
81-90	-0.10	1.35	0.074	0.941	-2.83	2.63
91-100	-1.30	2.24	-0.580	0.574	-6.25	3.65
OPT, operation preparation time ; DAA, direct anterior approach P<0.05, in bold

Table 3 Independent Samples t-Test And Welch’s t-Test Comparing ORT Of The Direct Lateral Approach And The DAA Technique At Different Cumulative Case Volumes

DAA Case Interval	Mean Difference	Standard Error	T Value	P Value	95% Confidence Interval
DAA Case Interval	Mean Difference	Standard Error	T Value	P Value	Lower Bound	Upper Bound
0-10	-64.11	10.37	-6.181	0.000	-85.17	-43.05
11-20	-29.11	6.81	-4.347	0.000	-43.52	-15.70
21-30	-20.11	9.63	-2.087	0.044	-39.67	-0.55
31-40	-8.61	9.71	-0.887	0.381	-28.32	11.10
41-50	-7.11	10.17	-0.699	0.489	-27.75	13.53
51-60	-11.61	9.95	-1.167	0.251	-31.81	8.59
61-70	-5.11	10.05	-0.508	0.614	-25.51	15.30
71-80	-3.61	7.77	-0.465	0.646	-19.67	12.45
81-90	0.89	9.47	0.094	0.926	-18.35	20.12
91-100	9.89	9.56	1.034	0.308	-9.52	29.30
ORT, operating room time ; DAA, direct anterior approach P<0.05, in bold

Table 4 Factors And Results Comparison Of 27 Cases Via Direct Lateral Approach (Group 1), 1-50 Cases Via DAA(Group 2), And 51-100 Cases Via DAA (Group 3).
Factors And Results	Group 1	Group 2	Group 3	P Value
Factors And Results	Group 1	Group 2	Group 3	Group 1 VS Group 2	Group 1 VS Group 3	Group 2 VS Group 3
Age（years）	70.81±7.68	72.12±7.73	71.8±10.01	0.481	0.658	0.858
Gender	7M 20F	10M 40F	12M 38F	0.550	0.852	0.629
BMI	21.79±2.18	21.34±1.72	22.06±2.01	0.317	0.597	0.058
Blood Loss（ml）	274.07±134.00	291.00±157.37	206.00±80.58	0.637	0.021	0.001
Blood Transfusion（ml）	492.59±654.53	488.00±324.28	464.00+198.73	0.973	0.826	0.657
Length Of Stay（days）	13.67±10.25	10.88±2.98	10.26±3.41	0.178	0.104	0.335
PT（min）	107.89±28.23	124.26±28.12	107.45±20.84	0.017	0.944	0.001
OPT（min）	26.00±3.35	35.54±5.75	28.35±6.44	0.000	0.039	0.000
ORT（min）	133.89±26.69	159.80±32.26	135.80±24.29	0.001	0.751	0.000
Complicati-ons(case)	1	3	0	1.000	0.351	0.241
Age, BMI, blood loss, blood transfusion, length of stay, PT, OPT and ORT were compared using F-test, independent samples t-test and Welch’s t-test, mean±Standard Deviation. Gender and complications were compared using chi-square test and Fisher’s exact test. F-test, α=0.1. BMI, body mass index; M,male; F,female;PT, procedure time; OPT, operation preparation time; ORT, operating room time; DAA, direct anterior approach P<0.05,in bold

No competing interests reported.

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Study on the learning curve during the transition from direct lateral to direct anterior approach in total hip arthroplasty : a consecutive one hundred and twenty-seven case series

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