diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index 3713eb6da60ac..f336eec8c4cce 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -4994,7 +4994,7 @@ def isin(self, values, level=None):
             self._validate_index_level(level)
         return algos.isin(self, values)
 
-    def _get_string_slice(self, key: str_t, use_lhs: bool = True, use_rhs: bool = True):
+    def _get_string_slice(self, key: str_t):
         # this is for partial string indexing,
         # overridden in DatetimeIndex, TimedeltaIndex and PeriodIndex
         raise NotImplementedError
diff --git a/pandas/core/indexes/datetimelike.py b/pandas/core/indexes/datetimelike.py
index 017dc6527944a..d6d8cb267e06b 100644
--- a/pandas/core/indexes/datetimelike.py
+++ b/pandas/core/indexes/datetimelike.py
@@ -398,16 +398,12 @@ def _partial_date_slice(
         self,
         reso: Resolution,
         parsed: datetime,
-        use_lhs: bool = True,
-        use_rhs: bool = True,
     ):
         """
         Parameters
         ----------
         reso : Resolution
         parsed : datetime
-        use_lhs : bool, default True
-        use_rhs : bool, default True
 
         Returns
         -------
@@ -422,8 +418,7 @@ def _partial_date_slice(
         if self.is_monotonic:
 
             if len(self) and (
-                (use_lhs and t1 < self[0] and t2 < self[0])
-                or (use_rhs and t1 > self[-1] and t2 > self[-1])
+                (t1 < self[0] and t2 < self[0]) or (t1 > self[-1] and t2 > self[-1])
             ):
                 # we are out of range
                 raise KeyError
@@ -432,13 +427,13 @@ def _partial_date_slice(
 
             # a monotonic (sorted) series can be sliced
             # Use asi8.searchsorted to avoid re-validating Periods/Timestamps
-            left = i8vals.searchsorted(unbox(t1), side="left") if use_lhs else None
-            right = i8vals.searchsorted(unbox(t2), side="right") if use_rhs else None
+            left = i8vals.searchsorted(unbox(t1), side="left")
+            right = i8vals.searchsorted(unbox(t2), side="right")
             return slice(left, right)
 
         else:
-            lhs_mask = (i8vals >= unbox(t1)) if use_lhs else True
-            rhs_mask = (i8vals <= unbox(t2)) if use_rhs else True
+            lhs_mask = i8vals >= unbox(t1)
+            rhs_mask = i8vals <= unbox(t2)
 
             # try to find the dates
             return (lhs_mask & rhs_mask).nonzero()[0]
diff --git a/pandas/core/indexes/datetimes.py b/pandas/core/indexes/datetimes.py
index 479e2023a00cb..11417e0b3317e 100644
--- a/pandas/core/indexes/datetimes.py
+++ b/pandas/core/indexes/datetimes.py
@@ -729,11 +729,11 @@ def _maybe_cast_slice_bound(self, label, side: str, kind):
             self._deprecate_mismatched_indexing(label)
         return self._maybe_cast_for_get_loc(label)
 
-    def _get_string_slice(self, key: str, use_lhs: bool = True, use_rhs: bool = True):
+    def _get_string_slice(self, key: str):
         freq = getattr(self, "freqstr", getattr(self, "inferred_freq", None))
         parsed, reso = parsing.parse_time_string(key, freq)
         reso = Resolution.from_attrname(reso)
-        loc = self._partial_date_slice(reso, parsed, use_lhs=use_lhs, use_rhs=use_rhs)
+        loc = self._partial_date_slice(reso, parsed)
         return loc
 
     def slice_indexer(self, start=None, end=None, step=None, kind=None):
diff --git a/pandas/core/indexes/period.py b/pandas/core/indexes/period.py
index ce2839ab9a8e1..4f92bb7bd7a87 100644
--- a/pandas/core/indexes/period.py
+++ b/pandas/core/indexes/period.py
@@ -622,12 +622,11 @@ def _validate_partial_date_slice(self, reso: Resolution):
             #  why is that check not needed?
             raise ValueError
 
-    def _get_string_slice(self, key: str, use_lhs: bool = True, use_rhs: bool = True):
-        # TODO: Check for non-True use_lhs/use_rhs
+    def _get_string_slice(self, key: str):
         parsed, reso = parse_time_string(key, self.freq)
         reso = Resolution.from_attrname(reso)
         try:
-            return self._partial_date_slice(reso, parsed, use_lhs, use_rhs)
+            return self._partial_date_slice(reso, parsed)
         except KeyError as err:
             raise KeyError(key) from err